For sound, I do everything by combining and editing samples, some I record myself, most are from freesound.org , you can search and filter by license. I've never had much trouble finding what I need with a CC0 license.
Also, listen to podcasts and youtube videos about foley. I recommend Twenty Thousand Hertz, episodes 12, 51, and 67. Maybe 27 and 30 depending what you're doing. Look up youtube videos for like, "how did they make the ___ sound".
Tools are useful, I just use audacity for sound effects because it's lightweight and does what I need, but they're not nearly as important as creativity and knowing how to make the sound you want. Which, all of that just comes from studying how others made sounds. For example, the enemy getting hit sound effect in one of my games is a stack of canvas being punched layered a few times, some vegetables being broken, and the sound of some wet, rotten meat being dropped on a cutting board that I happened across. That's a pretty classic combo for people/things being hit. Then sometimes you get a weird tip from a podcast or youtube video or friend, which is how I found out pigs scream, and that's the basis for most of the monster noises in Ocean's Heart, mixed with my dog growling.
Then all the processing of slowing down, or pitch shifting, or adding some synth bass behind it to make it really hit hard, etc.
Music is way more commonly understood. I use ableton to record and mix, but whatever you have will do. I think audacity is a bunch of trouble for music just because of some of its workflow stuff and I don't know that it snaps to bars, but it'd work fine too.
