Help with DeskCNC?

After some messing around with DeskCNC I still cant seem to generate
working G-code. Do you just import a STL, click on toolpaths and
select create? This seems a little too easy to to be true to me, i
tried it anyway but the code did not cut the part properly.

There is also a CAM mode in the DeskCNC program, after clicking on
this my opened part dissapears?? Is the demo crippled in this way?
I'm lost, can somebody give me some basic instructions on how i
should go about converting STL drawings to G-code? Thanks.

Mark