An additional kind of license is a Creative Commons license.
These are publicly available licenses that any rightsholder can choose to put on their own work. The licenses apply to everyone, and in every jurisdiction. They have some very specific requirements and restrictions that are generally pretty lenient and easy to meet. But beyond that, anyone can use their content - copy it, share it, create derivative works, and share those derivative works - for free and without having to get a license.
The Creative Commons was invented by some copyright lawyers back in the 1990s to help society cope with the strictness of copyright in the Internet era. It doesn't interfere with copyright law at all, but allows people to donate their works for free public use. It is not the same as public domain, because there is no legally enforceable way to put your works into the public domain. But it is the closest thing possible.
There are multiple Creative Commons licences, and each one has a different combination of permissions and restrictions. Here are the different options for permission or restriction, which can be recombined:
You can have many combinations of BY, NC, ND and SA.
What this means is that when you want to create a work that incorporates a Creative Commons work, you have to make sure that the license you want to put on your work is going to be compatible with the license of the work you are incorporating.
It gets more complicated when you want to create a work that incorporates two or more Creative Commons works. You will be restricted to the permissions of the most restrictive license.
This Creative Commons License Compatibility Chart is a simple visual way to understand license remixing, and it's also a great quick reference.
Just remember that if you are using Creative Commons licensed works, you absolutely have to follow the terms of the license to the letter, or else you void the license and then you're infringing on copyright.
Attribution is generally where people get hung up.
It is extremely important to give proper attribution, and there is one authority on how and where to do that: the Creative Commons website itself!