If your release contains copyrighted material, for example samples, upload the documentation here that proves you own the rights to it or are allowed to use it (such as a sample license).
Without the required license documents, music containing protected material can be rejected by the stores. Even if the digital audio fingerprint detects a possible copyright infringement in your audio, all relevant licenses must be available.
Uploading is optional and only necessary if your song contains third-party material. A checkmark will then show you that the license has already been uploaded.