I think Koz and I have answered this already.
Launch Audacity by double-clicking on audacity.exe.
Now you have a clean empty workspace to work in.
Decide if you want to back up by exporting WAV files periodically or by doing File > Save Project As… periodically. Do both if you want to be ultra safe
Do File > Save Project As… and give it a name that has the date and time (my_song_27aug13_0910.aup or similar). This has some theoretical advantage that when you start recording this data will not be temporary data but saved in the “my_song_27aug13_0910_data” folder. People can lose songs recorded into Audacity’s temporary folder if some ill-designed file cleanup program gets too aggressive about deleting temp files.
Record the first track. As soon as you press Stop after recording, File > Export as WAV. Then File > Save Project As… Give it a new name (my_song_first_track_27aug13_0915.aup or similar). Then you are working on the “my_song_first_track_27aug13_0915” project. Record the drums. Export that mix as WAV.
Apply a couple of effects. If Audacity crashes after that, it should recover correctly, according to how it sounds and how it looks on the screen. Orphan block files are expected and normally not harmful. They are audio data for undo/redo which you now cannot use. Audacity will delete those orphan block files on next project save. If the recovery is not correct, you can quit Audacity without saving changes then reopen Audacity. Go back to the last good backup (in this case, import the second WAV file). You just lost the couple of effects.
Run the effects again. If Audacity is still running, File > Save Project As… and give it another new name (my_song_two_tracks_and_two_effects_27aug13_0930.aup or similar). You are now working on that project and it’s saved.
Run another few effects that complete the first two tracks. If Audacity crashes and doesn’t recover correctly, quit Audacity without saving changes then open your last backup - in this case “my_song_two_tracks_and_two_effects_27aug13_0930.aup”.
You can also File > Save Project at any time. This saves your last changes to the same project file you are currently working on, overwriting the previous state that project had. It’s another insurance that you can get back to that last saved state. It is not a backup, if anything is wrong with that last project save.