Annotating the decompiled code is very much part of the workflow in using Ghidra, but the UI is not really intuitive. If you right-click on variables, function names etc there are a bunch of options for annotation. You can also edit the function signature, which can cause the decompilation to improve.

I know you can do various base address manipulations, but your case seems like it would be hard -- the base address is in the file, or has to be calculated.