In Audacity there is a gain slider on left side of a track. To increase volume i can use either gain or
Normalize the whole track to a certain level. Is there any technical difference in terms of increasing volume?
The process is identical, but one is tested, the other is not.
Gain will not test for overs, it will just clip if you add too much.
Normalisation will scan the entire track & only allow gain to be increased until the single loudest sample is at 0dBFS [or very slightly less if you want to avoid clipping on cheaper equipment. I've always used -0.3 as a 'safe margin'.]