With context, the meanings can vary a little. They both refer to a previous location. "Go back" suggests that the speaker is telling you to go back to a previous location. This location would be away from the speaker. So, leaving the speaker. "Come back" suggests the speaker is also asking you to return somewhere. However, this location would be where the speaker is. So, returning to the speaker. Examples: Person A: I forgot my cell phone at home. Person B: Go back and get it. So here "go back" implies person B is not going to go back with person A. So person A is returning to a previous location alone. Person A: Come back home after school. Person B: Ok, I will. Here person A is asking person B to return to a previous place where they still are. So, they will then be in the same place.

Come back, it uses when the speaker asks to someone to return from one place to the place he is Go back, it uses when the speaker asks to someone to return from one place to another