Hey Guys,
If are a beginner in mapping and you don't know how to map, then you should follow his guy's tutorials. They are really awesome and I learned mapping from his tutorials.
His tutorials are in german and I think that you can understand him even if you can't understand german.

Channel name on youtube: MrSchulzi1996

You should begin with this tutorial: https://www.youtube.com/watch?v=8Rgibz6-R9Y