The short word "Davai" (or "Davaite" in its formal version) is a very common one, and has a whole bunch of meanings: From "Let's", as in "let's do it" to "Come on!" and "Bye!". If you want to know all of them, just listen to this episode of Ruspod Shorts!
let's (do something)
Come on! (persuasion or do it faster)
OK, sure (when agreeing to an offer).
Let's go to the Kremlin.
Hello, informal (formal)