You kind of HAVE to learn map design on your own since its an art but, there are a few things that help me with map design.
You can start by writing down general area types and enemy encounters in a text document, but its certainly not required. I would recommend making an empty map with default textures and no monsters then detailing your map it usually leads to higher map quality and it's also done by other modding communities like the csgo mapping scene.
quick note though check for a thread in the search-bar before posting admins will lock your thread for seemingly no reason if there was a previous thread on the same topic.