There are loads of places to find music that you're welcome to use in your videos. The most searchable terms are "open source music" or "creative commons music", but you'll also find a quick reference list below. As videographers, we find ourselves scrolling through massive lists of music, searching for the perfect one, quite frequently. These are the one's we've come to rely on.
Youtube's Audio Library - Youtube's a great resource for this, you can use Clipgrab to pull the audio tracks, or if you sign up for Youtube Studio, there's an even more expansive option as well.
Free Music Archive - This is a massive, free to use, no sign in required archive.
Mugle.io - This is a project by an indie developer that scraped thousands of November's Youtube uploads and ranked the top 1000 Open Source songs by popularity.
Purple Planet Music - This is a few musicians that license their music for free to video creators.
Blue Dot Sessions - Another collection of indie musicians that offer their licensing for free.
BenSound - A huge collection, all written by one guy that's just passionate about free access to music.
SoundBible - Not music, but rather sound effects. Free to sign up for(doesn't spam and doesn't sell your information), but required for downloading.