First, make sure you don't have 2FA activated, or the Auto-creating token would not work. Make sure you create your PAT (Personnal Access Token) directly on GitHub.
Add a new credential:
And make sure also the "Verify Credentials" button returns a valid test:
Then:
Once that configuration is done, go to the project config of each job you want triggered automatically and simply check "Build when a change is pushed to GitHub" under "Build Triggers". With this, every new push to the repository automatically triggers a new build.
Note that there's only one URL and it receives all post-receive POSTs for all your repositories. The server side of this URL is smart enough to figure out which projects need to be triggered, based on the submission.
The url is not just under in "Git", but also GitHub:
See "How to Start Working with the GitHub Plugin for Jenkins" from Guy Salton.