Fork your open source project you want to contribute into your GitHub and clone your fork.
git clone git@github.com:dcnis/mockito.git
Show current configured remote repositories. The origin repo points to your fork on GitHub.
git remote -v
> origin git@github.com:dcnis/mockito.git (fetch)
> origin git@github.com:dcnis/mockito.git (push)
In order to fetch the updates from the open source project itself, you have to first add another remote usually called upstream.
git remote add upstream https://github.com/mockito/mockito.git
Now you have two remotes
git remote -v
> origin git@github.com:dcnis/mockito.git (fetch)
> origin git@github.com:dcnis/mockito.git (push)
> upstream https://github.com/mockito/mockito.git (fetch)
> upstream https://github.com/mockito/mockito.git (push)
Fetch new updates from upstream and merge them into your local main branch
git fetch upstream
git merge upstream/main main