The track volume control operates independently and in addition to event gain. If you set them both to -2 then the event is reduced 4dB. If you set the track volume to +4 and the event gain to -5 then the overall effect is -1. The slider near the preview window is merely for your listening enjoyment and has no effect on the project. So, if you want to affect individual volumes the track volume control isn't helpful as it affects the entire track.

There are a few things you might find very useful:

Right-mouse-button click on an audio event and choose Switches / Normalize. This increases the volume of that event up to the point where the loudest peak is at 0dB. This is useful if you have some clips that are overall low volume and can bring them up to the range of the louder clips.

Insert / Envelopes / Volume, when added to a track draws a thin blue line through the middle of the entire track. You can double-click on that line to add volume control nodes which can be moved up or down to vary the volume from point to point. The added benefit of these over event gain is that they can be used to raise the volume as well as lower it. Event gain only allows lowering of volume.

Effects / Wave Hammer. This is a simplified but very powerful compressor. You can set a threshold and ratio that automatically raises the volume of quiet parts and lowers the volume of loud parts. Experiment with it and see how it operates. Be careful though because overusing it can squash the life out of the audio. I tend to add it to the entire track and set it for something like threshold -3dB, ratio 9:1, auto gain compensate on. This evens out the loudest peaks and brings the overall level up just a bit without altering the dynamics of the quieter passages. Of course, what works for your project can be quite a bid different.