This repo holds common workflows that are used by other repos, check Reusing workflows docs from GitHub docs to learn more you they are made.
Workflows here can be called as described in the Reusing workflows docs. Also, you can add them easily to your repo by using starter workflows.
Reusing workflows docs describes how to add new workflows to this repo. After adding your workflow you will need to add it as a starter workflow as described in the creating starter workflows for your organization docs to make it available to other repos.