The develop branch represents the latest dev version. This is what you want to fork and base your feature branch on.
Branch names should use the following pattern.
fix/ = fix an existing issue
update/ = update an existing feature
add/ = add a new feature
remove/ = remove an existing feature
Some examples are add/sleep-timer and fix/notifications-crash.
When you are ready, please, spend time crafting a good Pull Request, since it will have a huge impact on the work of reviewers and testers.