TWIGHTLIGHT= The title of a novel about a girl (Bella) who falls in love with a good vampire (Edward Cullen). The book has been a worldwide bestseller and the trilogy has been taken to the movies. The word "twilight" literally means "two lights", and it refers to the time of the day when we are between "two lights" (day and night), that is, just between dawn and sunrise, and between sunset and dusk.

WAIT= We use this when we just stop and think about how wrong or stupid is what we just said.

SUBMIT= If a person submits something, they send it to somebody for judgement or consideration. On the Internet, when you submit something to a website, you send it there in the hope that it will be published, read or dealt with in the right way.

SWAP= Exchange, trade.

ALEX DAY= Also known by his nick "nerimon", is a friend of Charlie. His YouTube channel is very famous (at least in England) and he is also a pop singer.

A SERIES= Notice that this word ends in –S but it's singular.

ON YOUTUBE= Notice the preposition ON when we refer to the television or the Internet (and Youtube is both).

FAMILIAR WITH= If you are familiar with something, you know it (probably quite well).

HAVE A GO= (at something) Try.

CARLISLE= /kɑ:laɪ/ This word has got a strange pronunciation (unless you realise that it comes from carl+isle), so Charlie mispronounced it first (he said /kɑ:sli:/), and they he decides that it's a difficult name, so he's just going to pronounce it Carley /kɑ:lɪ/, because it's a more common name. So for the rest of the video, he will always read Carley instead of Carlisle.
Carlisle is a male vampire (a father figure for Edward Cullen), but because Charlie is not familiar with this name, he is not sure if the character is male or female. When he first mentions Carlisle, he thinks it's a female (so he says "I'm just gonna call HER Carley"), but then he realises it's a male because the writer says so. But anyway, Charlie will switch from he to she inconsistently throughout the video, and most of the time he will call Carlisle a "she", forgetting he is a man (obviously, that name sounds quite female for him).

THE WAGGONER= Wagonner is an English painter from the 17th century. He painted landscapes. So "the Waggoner" refers to a painting of Waggoner that the Cullens have on the wall (this is clear in a fragment of the text omitted by Charlie). In the same way that we can say "a Picasso" referring to a painting by Picasso, "the Waggoner" is the painting by Waggoner that you can see here on the wall. From the missing text we also learn that the Waggoner they talk about is a view of the city of London. The text in the novel goes:
Edward pulled me toward the far left side, standing me in front of a small square oil painting in a plain wooden frame. This one did not stand out among the bigger and brighter pieces; painted in varying tones of sepia, it depicted a miniature city full of steeply slanted roofs, with thin spires atop a few scattered towers. A wide river filled the foreground, crossed by a bridge covered with structures that looked like tiny cathedrals.
"London in the sixteen-fifties," Edward said.
"The London of my youth, " Carlisle added.
CASUAL= If you do something in a casual way, you do it as if it is not something important and you didn't think about it.

AUDIBLE= Something audible is something that you can hear.
- My heart had an audible reaction = When he touches me, my heart reacts beating loudly so you can hear it.

EMBARRASSING= Something embarrassing makes you feel uncomfortable and shy.

SEE?= Can you understand?

APPARENTLY= We often use this word in conversation to mean that the statement we are saying is true, or at least it seems true. But English speakers (especially British) overuse this word a lot and very often it doesn't really mean much.

HEARTBEAT= The beating of your heart. The heart is always moving, pumping blood, and that movement and sound is called "beat" or "heartbeat" to be more precise.

SCARY= If something is scary it makes you feel afraid.

I MEAN,= A very common conversation filler. We use it when we want to explain better something we just say, so that you can understand. Lots of people also overuse this phrase to the point that sometimes it doesn't mean anything at all, just a filler.

H*** CR**= A very rude expression to express surprise or disgust.

WHAT IS THAT WITH YOU?= (col.) What's the matter with you? (we use this expression when we are shocked or disgusted at what somebody said or did because we thing their behaviour was totally wrong or inappropriate) = Are you crazy or what?

DAWN ON= If something dawns on you, you realise it, you understand it or you have this idea on your mind.

I HAVEN'T JOINED THIS BOOK= Charlie is reading a chapter of Twilight right were his friend Alex Day had stopped, so he has "joined the book" at chapter 16 (he has joined with Alex there).

VAGUELY= Not very clear; remotedly.

IN THE SIXTEEN-FIFTIES= In the years 1650 to 1659.

YOUTH= The period of your life when you are young.

FEET= Plural of foot as a unit of measure. One foot equals 0.3048 metres, so Carlisle was probably 1 or 2 metres behind them.

IF SOME OF YOU HASN'T READ TWILIGHT= "Some" is a plural word (when used with countable nouns) so the verb should be plural (haven't). Alternatively, Charlie may have a singular idea on his mind at that moment, thinking of just one person who maybe hasn't read the book (we can use SOME with a singular noun to mean something not known, e.g., "some John is asking for you"), so he might have agreed his verb form according to his singular mental idea and not with the plural grammar form.

BACK STORY= Your back story is your background story, your history, the story of your past life, especially when it's going to help explain something about your present situation.

HOWEVER= Nevertheless, but, although. This word is a free connector, which means that it joins two different sentences in meaning, but both single sentences remain single and independent. However (as all free connectors), is usually separated from both sentences through a stop and a comma: ++++. However, ++++.

I DON'T GET WHY...= I can't understand why...
In colloquial speech we often use GET instead of UNDERSTAND:
- Get it = Do you get it? = Can you understand it?
- Sorry, I don't get it = I'm sorry, I can't understand it.

THE CHANNEL= The English Channel, the strait of sea separating England from France.

ARE ON THE SAME PAGE= (expression) If two people are on the same page, they think in the same way, they agree (like two people reading the same page from a book).

CHUCKLE= To laugh quietly or to oneself.

DARKLY= In a dark way. The word DARK may refer to the absence of light or to something evil, bad.

,TECHNICALLY,= Theoretically, in theory.

AS YOU GO= While you are going.

I WASN'T SOLD ON HIS LIFE OF ABSTINENCE= I didn't accept his life of abstinence (I wanted to drink people's blood).

CURBING= To curb something means to check it (stop it), restrain it or control it in some way. The doctor (Charlisle) didn't let Edward to quench his appetite for blood.

APPETITE= An instinctive physical desire, especially one for food or drink.

I WENT OFF ON MY OWN FOR A WHILE= I left and lived my own life for a short period of time.

IT'S IMPLIED= It's implicit. It is not said, but we can easily deduce it from what they said. If you imply something, you don't say it clearly but it is an obvious deduction from what you say.

INTRIGUED= If you are intrigued by something, you feel curious about it and really want to know more about it.

MENTAL= (col. BrE) Crazy, with a mental problem.

I GUESS= I suppose.

 HE CAN'T HELP IT= If you can't help it, there's nothing you can do about it, it's impossible for you to control.

INSANE= Crazy.

I'VE COME TO THE REALIZATION= (formal) I've realized...; I've come to the conclusion that...; now I believe...

DESERVE EACH OTHER= If you deserve something, you are worth it, you merit it. Charlie thinks they deserve each other because Edward is a monster and Bella is crazy, so they are a good match.

WALKS IN= Enters the room.

AND IS LIKE "DO YOU..."= (col.) And more or less says something like "do you...

IMPONDERABLE= Immense, impossible to measure.

JOY= Happiness.

CHARLIEISSOCOOLLIKE= It's the nick of Charlie on YouTube, it means: Charlie is so cool-like. The "like" at the end doesn't mean anything; his mother Lindsay uses the nick "liliesarelike" (= lilies are like) so either he took the final "like" from his mother or she from him, a kind of family name.

MAKES YOU LIKE COOL= "Makes you more or less cool" (like: preposition) or "Makes you like cool things" (like: verb).
(based on "Charlie is so cool like" -- "like cool").