1. to serve (in context of waiting tables)
2. to operate, handle (for devices and machinery)
3. to help/serve oneself ("sich+Acc bedienen (an)" - colloquially often used for digging in )
A fun look at the meaning of "dienen", its origin and what earning money has to do with a user manuel and a buttler.
Vocab:
dienen, der Dienst, der Diener, bedienen, die Bedienung, die Bedienungsanleitung, verdienen, der Verdienst,