Learn French: Tu peux nager dans la piscine maintenant.

Pouvoir (can / to be able to) is a highly irregular verb. While most verbs in the tu form end in an -s, a few very common irregular verbs like pouvoir and vouloir (to want) end in -x for both the je and tu forms (je peux, tu peux).

Why isn't the verb nager conjugated to match tu?

In French, when you use two verbs together, only the first one is conjugated. Because peux is already conjugated to match tu, the second verb nager (to swim) must stay in its unchanged dictionary form (the infinitive). This is just like English: we say 'you can swim', not 'you can swims'.

Do I pronounce the 'x' at the end of peux?

No, the -x is completely silent here, so peux sounds a bit like 'puh'. The 'x' would only make a 'z' sound if the very next word started with a vowel (which is called a liaison). Because nager starts with a consonant, the 'x' stays silent.

Why do we use dans for 'in' here instead of another word like en?