step 1) open docs-folder and read manual and community guide
step 2) search all these subforums back to page 30 and collect everything that seems interesting for you, especially tutorials and how-to-do´s in the threads
step 3) use your media inside fpsc to get knowledge about handling, fpsc-typical failures with media, entityplacement, interaction etc.
step 4) learn to retexture with any type of graphic program, most common is GIMP (free) or photoshop
step 5) learn model-programms (you will find them with step 1&2) to build your own things and how models get uv-mapped.
step 6) learn how to create your own textures in a graphic prog.
gz & welcome