How do I start the program?

1. You go to releases.
2. Select your version (by clicking on the big blue text).
3. If not already opened, open the dropdown "assets" on the bottom of the page.
4. Look for the file in the format "MCDatapackCreator-X.X.X(-alpha/beta).jar" ("alpha" or "beta" may not be present)
5. If it's downloaded, you're done! Just execute it and you can start creating data packs!

If you've gone through this guide, you may find this one useful.