The basics of how a compressor works.
It’s essentially an invisible hand automatically raising and lowering the volume of a track. The idea is to lower the volume on the loud parts so that you can hear the quiet parts better.
Learn with whatever you have available.
You’ll find people in online forums fighting over whether one plugin is better than the other, or whether you can get as good of a sound out of plugins as you can with hardware, or any other sort of nonsense. Don’t listen to them. Whatever you have in your DAW is good enough to record. If you are just starting out, your lack of experience and knowledge will eliminate any possible advantages of using an expensive plugin or outboard gear.
Use your eyes and your ears.
The most important thing is what the track sounds like. Things like -db and all of that are simply a way for me to talk to you about some starting points. Can you record a platinum record with a vocal getting -20db of compression? Sure, it’s been done. Don’t take any of the tips that I give as steadfast rules—they are simply starting points.