I know when to use them however I can't really explain why. Will you help me?
The meaning of "get to someplace" is to reach that place. Compared to that, "go to someplace" emphasizes the progress, the movement toward, rather than reaching it.
If you say
I need to go to the meeting now.
you essentially state that you need to leave your current location.
If you say
I need to get to the meeting now.
you state that it's time for you to be at the place where the meeting is held.
The first sentence would mean you need to reach a place, an event, or a person. The second one means that that you have to leave, but not necessarily have to go somewhere else. Therefore, you can use the first sentence when you need to go somewhere else, and the second one when you have to leave your current location.
Get to may imply some sort of urgency, or that there's difficulty in reaching a certain place.
Go to implies that you need to leave the place and continue the progress towards the destination (if there's any progress at all).