In order to sync your local project on your computer to GitLab you will need to install and setup a Git client such as SourceTree.
For a list of Git Clients that are compatible with GitLab: https://about.gitlab.com/applications/#gui-git-clients
Alternately, if you prefer using Git via the command line, you can find helpful documentation here: https://gitlab.blinkm.io/help/gitlab-basics/start-using-git.md
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