You may have heard people tell you to create metadata to go along with your data. The reason for this recommendation is so that your data will be understandable and usable in the future - either for you and your lab members or for a wider audience should you share your data outside the lab. There are many ways to document your data beyond using metadata, though, and more information on all of them are here. If you have questions please ask!
Keep a file with information about your project in the same folder as your other files. A rule of thumb is to write as much information as necessary to understand your data.