Clone: In case you just want to download it for personal use
Fork to your GitHub repository and then clone that version: In case you want to contribute back the changes you've made.
When you clone a GitHub repository on your native workstation, you can't contribute back to the upstream repository unless you're explicitly declared as "contributor".
That's because your clone could be a separate instance of that project.
If you want to contribute to the project, you can use forking to do it, in the following way:
First, clone the GitHub repository on your GitHub account (that is the "fork" part, a clone on the server side)
Now, you can contribute commits to it GitHub repository (it is in your own GitHub account, so you have every right to push to it)
Also. signal any fascinating contribution back to the original GitHub repository (that is the "pull request" part by means of the changes you made on your own GitHub repository)