First, adjust Boost 11 while the audio track is playing so you can see the resolts of your changes. The OUTPUT knob on the right sets a limit to how loud the audio can go. The BOOST knob on the left increases the volume of the audio. Let's say you have an audio track with some very loud transients compared to the rest of the audio. Set the OUTPUT knob to the max volume you want the track to be. 0 db is the loudest the track can get and may be a little too loud for most applications other than mastering the final mix. I generally use -6 db on a track.
How much boost you add depends on how loud the track already is. You can tell when you have boosted the audio past where you have the OUTPUT set when you see the middle REDUCTION meter working. It will show, in db levels, how much it is limiting the material. If you see large RED peaks in the
waveform IN window under the BOOST knob you will know you have seriously changed the dynamics in the audio... which may or may not be what you had intended.
When I use Boost 11 it is usually to knock down a few transients without affecting the overall sound too much. So, I boost the level until I see the reduction meter working just a little. I suggest a bit of practice with it so you can learn to associate what the meters show and what you are hearing.
If you use Boost 11 on a track and the Reduction meter is showing reduction with NO boost, then you can control the level of limiting by raising the Output level.
I routinely normalize my audio to -6 db after recording, so I use -6 db as the Boost 11 output level. Then I slowly raise the Boost level from 0, watching the
waveform IN window and the Reduction meter until I'm seeing and hearing the sound I want.