Learn French: Elles n'aiment pas l'école.

The negative word ne drops its 'e' and uses an apostrophe when the verb right next to it starts with a vowel, like aiment. This is called elision, and it makes the phrase flow more smoothly when spoken.

Where exactly do the negative words go in this sentence?

In French, basic negation acts like a sandwich around the conjugated verb. The ne (or n' in this case) goes right before the verb aiment, and the pas goes right after it.

Why is the word 'the' (l') used before école when the English translation just says 'school'?

In French, when you talk about your likes and dislikes using verbs like aimer (to like/love), you always need a definite article (le, la, l', or les). So to say you like or dislike school in general, you must say l'école (the school).

How do I pronounce aiment? Do I say the -ent at the end?

No, the -ent ending on French verbs for the 'they' form is completely silent. You pronounce aiment exactly the same as the 'I' or 'he/she' forms: it sounds like 'em'.