i don't know bout newer truspace versions, but in 5 you can click the trash bin in the bottom left corner and a huge slab of buttons will appear. every button ts has as far as i can tell. then you have a tiny description of what it does/it's name in a dialogue box (which for me is on the bottom)
from that you should be able to find the material editor.
get your .bmp textures into the truespace texture folder with explorer and then add all of them to the texture library by opening the the library and selecting the very first default texture (for me it was a "caligari" texture) and click on the preview in the "colour" extention window from material editor.
a new window opens with previews of all the textures in the texture folder. right click any texture and click "add all to library". this will add all the textures found in that folder to the library. you can then use them by opening the library and selecting one.
to set a uv map for a model, look for a button that has a blue and white checked pattern on some type of object (a cube for cubic mapping) it in the slab of buttons. click it and you will then be able to apply textures.
hope this helps, but in my opinion, the best learning method is fiddling untill it works.
