I thought I'd make a quick summary for anyone who's interested in using my tracks in their own projects.
Singles / Personal albums
License: CC 4.0 Attribution / Royalty-free
You are free to do whatever you want, even for commercial projects, as long as you credit me as the author of the chosen music. If you're planning on uploading your project on Newgrounds, you're not required to share revenue, though it would be nice.
Example 1: "Hi can I use your track for my awesome creation?"
Yeah, just credit me and we're fine.
Soundtrack albums / Video-game related music
You are free to use these tracks for your own projects, as long as you credit me as the author and you don't make money out of it. Furthermore, if you modify or remix upon these works, you have to use this same license. Again, if you're planning on uploading your project on Newgrounds, you're not required to share revenue, though it would be nice.
Example 1: "Hey I'm making this game/mod, can I use this?"
If you're planning on profiting from either its soundtrack or the game/mod, then you may NOT under any circumstance use those tracks.
Example 2: "Hey can I use this track for my cat hairballs awareness student film?"
Again, we're all good if you're not planning on making any revenue from it and you credit me.
License: All Rights Reserved / Generally One-off payment - Royalty-free
Read their licensing rules upon purchasing my audio. Crediting isn't necessary though it would be nice. There's no need for contacting me for permission. You paid for it, you get to use it. Simple as that. Audiojungle offers a variety of specific licenses you can buy based on different uses.
License: All Rights Reserved / I don't own shit
Don't use these tracks, period. I don't own the intellectual property belonging to the original content creator, nor I am able to monetize upon it. Neither should you.
License: Varies / Typically CC 3.0 (see above)
As a rule of thumb, since these tracks don't include just me, you may only use them for non-profit projects. Furthermore, you should credit me and whoever else is involved as authors.
If you still have any doubts or would like to share royalties or any other inquiry, feel free to shoot me a PM. Otherwise, it would be advisable to consult a lawyer.