This generates a checksum for text you paste in — a config file's contents, a short script, a manifest — which you can compare against a previously recorded value to confirm nothing changed.
This isn't the right tool for verifying a downloaded binary file (an installer, an archive, a disk image) against a published checksum — that requires hashing the file's actual bytes, which a browser text box can't do for arbitrary binary files. For that, use a local command-line tool instead: sha256sum file.zip on Linux/macOS, or certutil -hashfile file.zip SHA256 on Windows.