There are several places where you can find sound effects and music beds for your project.
Before we start, it is important to understand one point about licensing for videos that catches people off-guard. A Creative Commons - No Derivatives license will not work for video content. Read this, right from the Creative Commons site:
Most importantly, you need to use music that is **not** licensed under a No Derivative Works license. This means that the musician doesn’t want you to change, transform, or make a derivative work using their music. Under CC licenses, synching the music to images amounts to transforming the music, so you can’t legally use a song under a CC No Derivative Works license in your video.
Here are some resources:
Soniss realesed a 10+ gigabyte sound effect library in 2015. You can get the library here. It has been extremely popular, so you may need to obtain the archive via bittorrent (torrent link)
Freesound.org is a collaborative site with tons and tons of location sounds, sound effects, samples, sound packs. You name it. Much of the content is under public domain / creative content licensing.
Youtube Audio Library has music and sound effects that are cleared for use and royalty free. These were released to help content creators ensure that their sound would not trigger a content id warning on youtube and prevent monetization of the video.
Incompetech has a large repository of Music beds. Created by Kevin MacLeod, he has a very generous license for his music, with an emphasis in his FAQ of Anyone can use any of my music in any project.* _***You do need to attribute correctly if you are using the Creative Commons license **or pay for the no-attribution license, if you choose that one. _He covers lots of genres and moods.
Bensound also has a large genre / mood based catalog of sounds. However many are licensed under a Creative Commons license with No Derivatives, which can be problematic if you want to use them with video content. Make sure you read the FAQ for information.
The Free music archive has some music available, but you need to go to the details for any given song to check the licensing of it, much of it is Non-Commercial, so it is problematic should you want to use it in any commercial voiceover.
Finally, a YouTube search can often reveal a sound effect that is just what you were looking for that has a download link. Again, always try and vet any licensing for any commercial project.
The world of licensing can be tricky to navigate. You can always pay for a license to a track at any of the many, many royalty-free repository sites, while finding free-to-use is more challenging.