THE END OF DAYS= The destruction of the world (an expression taken from the Bible, esp. from the book of Revelations or Apocalypse)

MIST= fog (a cloud on the ground). The difference between MIST and FOG is not very clear in everyday usage, so they are often interchangeable. In fact, the mist we can see in this movie is actually fog, not mist. Mist is more like vapour, not so thick and more down to the ground, while fog is more like a real cloud, thicker and higher. If you really want to be strict about it, the World Meteorological Organization has arrived to a standard in which we can say "fog" when the visibility is reduced to 1km or less. If we can see further than 1km then it’s mist.

SOMETHING IN THE MIST= There is something in the mist

SHUT= close

WHETHER= if. But not the conditional if (if you come, I’ll tell you). It is used when we have to choose between two option: "you’ll go whether you like it or not" = you’ll go if you like it or if you don’t like it.

MAN-MADE= made by man, artificial

I DO KNOW= This DO in an affirmative sentences is used to emphasize the verb (= I really know)

I DON’T KNOW, LIKE SOMETHING WAS LIKE, PRESSING AGAINST THE DOOR= Here we can see the use of the conversational preposition LIKE twice. It often means nothing, but sometimes we use it to express the idea of "more or less but not exactly".
"Something was like pressing" = "something was pressing, but not really pressing, though it seemed like it was pressing or something similar to pressing but in fact I have no idea of what was exactly happening". As you can see, the expression "Something was like pressing" is much shorter and convenient

PRESS= push

GONNA= going to

SEEK= look for

GOIN’= going

IT’LL LET US KNOW YOU AT LEAST GOT THREE HUNDRED FEET= if you tie the rope around your waist, we will know at least if you can walk 300 feet away from the supermarket or you are killed before that.
1 foot= 0.3048 metres
The plural of FOOT is FEET (the couple of things we use for walking), but when it’s the unit of measure, people use FEET but also FOOT (a rope 12 foot long/ 12 feet long). If we’re talking about the height of a person we usually say FOOT (e.g. "he’s 6 foot tall")

THE JOKE WILL BE ON ME= an expression meaning "I will suffer the consequences"

TO TAKE SIDES= to choose in what group of people you want to be (when there are different groups of people with different opinions or projects)

THE SAVED AND THE DAMNED= people who are saved (and will go to heaven) and people who are damned (and will go to hell). These are two of the few cases when we can use "The + adjective" meaning "that certain group of people" (other expressions are: the poor, the rich, the disabled, etc., but we can’t say, for example, "the tall")

THE GOOD BOOK= The Bible

SOMETHING GOT IT= something entered the room

GUYS (AmE)= a colloquial word meaning "men and women". But the singular "guy" is only used for men.

FOR ALL WE KNOW= it means that we have no information about it so any possibility may be true.
- where’s John?
- John? He could be in China for all I know (= I have no idea where he is)

IT WOULDN’T MAKE US ANY LESS DEAD= if we die, it is not important if the mist is only around the supermarket or it spreads all over the world.

THE MONSTER GET ME= the monsters capture me.