the coolest thing you're not using!
The Community Guidelines outline how to build and maintain your repo so that it fosters a good community of contributors. It will walk you through important steps like setting up issue templates.
These labels are great for helping users either who have downtime or maybe are new that want to contribute.
Repos often represent either an entire app, or a system that is part of an app. In either case, milestones represent significant events in the life of a repo. Where this is a product/app milestone, or a new feature within a supporting system. Milestones are a great way to represent chunks of work that add new capabilities.
Projects can be related to a single repo, or an entire organization. If you are using organization projects, then you can include issues from any repo within that organization. Either way though, notes can reference issues anywhere that the user has access to. So, notes are perfect for defining requirements. Take a look at the sample project in this repo (check out the view for all projects too). Check out the following articles to help you get started!