Пити - to drink, П'єте - you (plural) drink, П'ю - I drink. Всі п'ють - Everybody drinks :)
I think it's either, whichever fits the context. So 'drinking' would fit best for 'I like ... juice'.
Alternatively, 'Я пити сіт' can be 'I drink juice' or 'I am drinking juice'.
Wouldn't "I drink juice" be "Я п'ю сіт" (edit: ups, a typo, I of course meant сік) though?
Yes. Я пити сік is not a grammatical sentence. It needs to be Я п’ю сік.