Ok first thing you need to understand is the difference between mixing and mastering. When you are mixing you are working with separate audio files like “guitar left”, “guitar right”, “vocals” etc. You are mixing each file separately, so for example you eq and compress “guitar left” and you are satisfied with it and then you move on to “gutiar right” and you eq it and compress it as well and so on until you mix every file in your song. (there is obviously more things to do than just eq and compress but I’m just trying to keep it simple so you can understand). After you’ve mixed every file and you are happy with it you export the whole thing into one single audio file. That file would be the mixed version of your song. Then you would put that file into your daw and you would master it. Mastering is just polishing your mixed version and making it louder. So you would use an EQ and maybe boost 0.5 or 1dB on low end to make it “bigger” or “fatter” and maybe boost the same amount in the high end to make it “brighter”. You don’t boost for example 5db when you are mastering cause that’s too extreme because you are not boosting just one file or instrument but you are boosting the whole song and if you would for example boost 5db on the high end to make the guitars stand out, you would also boost the cymbals and crashes and that wouldn’t sound very good. So that’s why you want to boost in small amounts when mastering cause you are just polishing the whole thing. The most work is done when mixing. Also in mastering you would want to compress your song to “glue” it together and then maybe you could add a tape emulator to make it warmer. The last thing you do when mastering is LIMITING. Limiting is just increasing the volume of your song to a commercial level so that it doesn’t sound too quiet. When you are done limiting you export the file and you have a mastered song.
As for the eq and compressor settings, Rick Beato made videos about that so that should help you: https://www.youtube.com/watch?v=EAGC2fUAU1M
but keep in mind that: NOT EVERY GUITAR, KICK, SNARE, BASS, VOCAL…. SOUND THE SAME. Every sound is different so if you read that you should boost the kick on 50Hz that doesn’t mean that every kick should be boosted at 50hZ. Some sound better when you boost them at 60 HZ. SO nothing is written in stone but the cheat sheets will help you where to look.