Hello Mrdodobird!
The first thing I'd recommend is to look around for tutorials. Depending on the scale of map you want to make (satellite style atlas? continental or regional scale? One settlement and its environs? A single building/dungeon/complex?), there'll be various methods people have discovered out there.
Personally, I hashed something out from a tutorial for starfields, in which I mashed and overlayed multiple stock textures from the internet to create a combination heightmap and satellite-imagery texture. The map itself i worked out by toying with this map to identify coasts, woodland and mountain.
There's also tools out there, like Inkarnate, which can do the map-building for you. Have a look around the web and see what takes your fancy.