Get back = return FROM a place
Go back = return TO a place

“I got back from work late last night” (I returned FROM work late last night)

“We went back to the restaurant because the food was so good” (We returned TO the restaurant)

Other meanings

get back to sth = to start doing or talking about something again

“I would love to talk but I need to get back to my work”

get something back (from someone) = receive something that is yours from someone (after lending for example)

“I let my brother borrow my car but I haven’t got it back from him yet”