Learn Dutch: Je mag hier niet stoppen. - You are not allowed to stop here.

When you use a modal verb like mogen (to be allowed to) in Dutch, it takes the normal second position in the sentence. The other verb, which is stoppen (to stop) here, gets pushed to the very end of the sentence in its full dictionary form.

Doesn't "must not" translate to moet niet? Why do we use mag niet?

This is a classic trap! In Dutch, moet niet usually means "do not have to" (a lack of obligation). If you want to say that something is strictly forbidden or "must not" be done, you use mag niet (literally: "not allowed to").

Why is the verb mag instead of "magt"?

Mogen is an irregular verb. For the singular pronouns (ik, jij, hij, zij, het), the present tense form is just mag without a -t at the end.

Why does niet come after hier instead of right after the verb mag?

In Dutch, niet (not) usually comes after words that indicate a specific place or time. Since hier (here) tells us the place, niet is placed directly after it.