Assuming this is a single track recording:
Before you do the final “Export” step, select “Normalize” from the effects menu.
Tick check both boxes, and enter the number 1 in the text box, then click OK.
Unless there are any loud clicks or thumps spoiling your recording, you should now see the overall volume level is close to maximum.
If you have multiple tracks, play the project and watch the playback meters - adjust the volume sliders on each track as necessary.
When you record, you should set the levels in the Recording levels in the Windows Mixer (loudspeaker icon near to the system clock) so that you have a strong, but not overly loud recording.
Here is a screen shot of three stereo tracks:
The top stereo track has been recorded too quietly, the middle track is too loud and will be badly distorted, the bottom track is about right.
After the “good” recording has been normalized to -1 dB it will look something like this:
No that’s not necessary for MP3’s. LAME (the mp3 encoder) will automatically make any bit depth changes that are necessary.
If you want to make an audio CD, then you should export as 16 bit 44100 Hz WAV (Microsoft PCM) format.