How do I install mods?

[Wolfbane]

Sounds like a dumb question but I just want to make sure I do it right. Also what are good sites to use?

[🐉 Ðŗąçø 🐉]

http://forums.x-plane.org is the obvious one. Sign up, go to downloads and get what you want.
To install plugins, download a zip file, unzip it and then put it in the folder steamapps\common\...\X-Plane 11\resources\plugins.
For aircraft, follow the path above, but use the aircraft folder instead.