Need a Crash Course on how to make a Level/Terrain

Hey! I don't post often, but I've been around here for a while. Before you ask, I DID search for a thread with a bit of a tutorial, the content creation wiki is pretty useless. I have been mapping on SDK's Hammer(mainly for csgo), and I feel like mapping here may be similar. Source is an old engine, and this is a new one, meaning that learning level design for this game would probably be pretty great. So, Because I like this game so much, I'm really interested in making a map for this game.

However, I can't begin without knowing what program I should use to map, how to import the game's materials/resources(unless they're already included), how to create your own resources/materials, and how to compile/convert the map so it's playable in game.

If someone could help me out here I'd greatly appreciate it. If I missed a thread that already covers all this, please calmly link it to me. Thanks in advance!