To express obligation or strong advice in English we can use HAVE TO or MUST

MUST
This is a modal verb, so it doesn't use DO or adds an -S for the 3rd person singular of the present:

- You must stay here
- Must she come with me?
- No, she mustn't

HAVE TO
This is a normal verb, so it uses DO and has an -S in the 3rd person singular of the present.

- You have to stay here
- She has to go
- Does she have to come with me?
- No, she doesn't

In modern English, "must" and "have to" usually mean the same, so you can use both:

Sorry, I have to go = Sorry, I must go

But the verb MUST sounds stronger than HAVE TO

---- COLLOQUIAL FORMS ----

HAVE GOT TO
This form is more common in Britain. It's a normal verb, so we use DO for negatives and interrogatives
- Sorry, I've got to go
- Do you have to go now?

GOTTA
This form is more common in America.
- Sorry, I gotta go
(gotta = have got to)

NEGATIVE OPTIONS
- You mustn't tell a secret = don't tell a secret!
- You can't park here = you mustn't park here
- You shouldn't park here = it is not a good thing for you, this is my advice

Compare:
- You can go = permission (you can go if you want)
- You can't go = prohibition (stay!)
- You have to go = obligation (go!)
- You don't have to go = no obligation (you can go or you can stay)