Download blender, if you'll be working with blender in various locations which may not have an internet connection, download the manual to your computer, extract the zip and open index.html. Now pick up a shortcut pdf
When creating maps with blender, this is mainly referred to as modelling so start with that section first at least understand object and edit mode. Next read through the mesh section and tool section. At this point you should have the bare minimum to get started
learn your tools
extrude: pull the side of a 3d shape out while creating a new shape at the same time
3d cursor: a point in space which is denoted by the white and red dashed circle, it is used as a reference point when you use various tools, use ctrl+c to recenter it at the origin of the space
rip region: allows you to break geometry such as disconnecting edges
knife: allows you to cut into geometry
spin: rotate and duplicate an object in a circular pattern
must know shortcuts
Before you do anything else, go to preferences and then to keymap, search for "search menu" and create the binding shift + space that maps to it.
This will be the meta binding that allows you to figure out new things and do things quickly. Use shift + space to do whatever you want simply by searching for what you want to do.
ctrl+tab a quickswitcher for the different modes
camera
focusing the camera origin
If you've created an object and you want the camera to rotate about the center point of the object, use the command frame selected.
creating shapes
using the cursor
the cursor acts as a spawn point to every shape you create, therefore moving it to specific places before you create an object drastically speed up the creation of shapes because you don't have to move the shape as much after.
A good command to know is cursor to active which moves the cursor to the origin of the currently slected mesh.
selecting
None, selecting things that are similar use select similar, for example to select all faces of a shape which are on top you can select similar using normal
insetting
To inset one edge you can select two edges for which you want the edge to start and end at, then use subdivide to create the perpendicular edge. Next use edge slide to move the edge where you want it to be.
cutting into things
The main tools to use for this are the knife, knife project and the boolean modifier.
A common use case is to cut a circular object into something, to do this create a circle, then go into edit mode on the object you want to cut into and then select your circle as well, and then use knife project. After doing the cut you can delete faces.