Creating a git develop branch
You can list all of your current branches like this:
git branch -a
This shows all of the local and remote branches. Assuming you only have a single master branch, you'd see the following:
* master
  remotes/origin/master
The * means the current branch.
To create a new branch named develop, use the following command:
git checkout -b develop
The -b flag creates the branch. Listing the branches now should show:
* develop
  master
  remotes/origin/master
Changing branches
You shouldn't commit anything directly to the master branch. Instead do all your work on the develop branch and then merge develop into master whenever you have a new public release.
You are already in your develop branch, but if you weren't, the way to switch is as follows:
git checkout develop
That's the same way you create a branch but without the -b.
Making changes on develop
When making changes, add and commit as usual:
git add .
git commit -m "whatever"
The first time you push to your remote do it like so:
git push -u origin develop
The -u flag stands for --set-upstream. After the first time you only need to do it like this:
git push
Merging develop to master
Once your develop is ready to merge into master you can do it like so:
First switch to your local master branch:
git checkout master
To merge develop into master do the following:
git merge develop
Then push the changes in local master to the remote master:
git push
Done.
Deleting a branch
If you don't need the develop branch anymore, or you just want to delete it and start over, you can do the following:
Delete the remote develop branch:
git push -d origin develop
Then delete the local branch:
git branch -d develop
The -d means delete.