There's a good chance that you'll incorporate media that you find online into your project.
An asset is any material that you bring into your video. The footage you recorded is just one type of asset, but there are many others like images, sound effects, and music. So the first thing to ask before starting to edit is: Do I have all of the assets I need to finish my project? And if not, where can I find them?
For any media that you use that you do not make, consider whether you have permission to use the media. Basically, any media creator (this stands for photographs, videos, music - any kind of creative work) gets to decide how other people use that work, also called the usage rights. These decisions are dictated by what kind of copyright they apply to their work.
Usage rights help you find content that you can use above and beyond fair use. Site owners can use licenses to let you know if and how content on their sites can be reused. If you don't want to pay for the media, look the "Creative Commons" license. There are variations of Creative Commons, or CC, licenses: broadly, it breaks down into whether the artist has decided you can use for commerical or noncommerical purposes, and whether you can change the media or not. Most media sites will have a way to filter for CC-licensed media.
The term “public domain” refers to creative materials that are not protected by intellectual property laws such as copyright, trademark, or patent laws. The public owns these works, not an individual author or artist. Anyone can use a public domain work without obtaining permission, but no one can ever own it. Public domain works are generally older, but not always.
In an educational setting, like for a class project, most materials are available to you under the practice of "fair use." Fair use is a legal doctrine that promotes freedom of expression by permitting the unlicensed use of copyright-protected works in certain circumstances. In this case, fair use is because you're still learning and you're not making money off of the project. However, after you graduate, or even if you're working on an external internship during school, you need to know the usage rights of the media. Other examples of when you can use fair use include criticism, comment, news reporting, teaching, scholarship, and research.
You still need to cite all of your sources, even if they are fair use, CC, or public domain! Check this guide for resources on creating citations.
If this is all a little confusing, that's ok! The next page has resources and tools for finding CC-licensed and public domain works.
Note that these considerations are important for all media, but most people encounter them when trying to find music to use in their work. Popular songs are (very) copyrighted, and YouTube will not let you upload projects that use popular songs (or will take them down quickly), even if you're using them for a class project.
And, remember that the easiest way to avoid having to think about these things is to create your own media!