This is the 604th most frequent Italian word.
puoi
"Puoi" means "you can" (second-person singular of "potere").
In this sentence, 'puoi' expresses the option or possibility for someone to join, conditional on their decision.
Se vuoi, puoi unirti a noi per cena.
If you want, you can join us for dinner.
Here, 'puoi' is highlighting an ability or skill the subject possesses regarding swimming quickly.
Puoi nuotare molto velocemente!
You can swim very fast!
Here 'puoi' is used to form a polite request asking for assistance, indicating possibility or permission.