In my youtube videos, you'll hear audios, and see images, videos and i'll do a quick little explanation how to get them for free (most of the time).
I dont nothing special but for images and videos I just download them from Tiktok, sometimes Youtube or just a quick google search for an image.
For audios thats where it gets tricky but for meme auidos or anything of that sort I usually get them from Youtube or tikoks.
For audios like actual songs I can't explain how to get them for free but there are companys/websites that give you licenses to use songs in your videos without getting in trouble!
Finzar
I used to watch a lot of videos to understand how to edit and I think one of the best Youtubers who helped me out was Finzar.
Storezar
I have also gotten some stuff from his store like preset packs which makes it so much easier for me to edit videos.