"Đi" = let's go or should" when it is used as a final particle in the sentences.
"Đi" = "go". Also "Đi" = let's go or should " when it is used as a final particle in the sentences.
For example :
Chúng ta đi đi = Let's go, we should go
Bạn đi ngủ đi = You should go to sleep.