This page covers how you can save what changes you've made to the current branch by committing them, which keeps the changes tracked in the branch history. This way you can roll changes back, do comparisons, or keep work separated out.
Using TortiseGit(Windows only)
Tortisegit is a Windows shell-integrated git ui tool to make it easier to work with git. If you've used tortisesvn, it's pretty much the same but git-flavored instead. If you don't already have tortisegit, you can get it here
Click RMB and clicking the "Git Commit -> "BranchName"" option. You'll get a menu that shows what files have been changed, and prompting a commit comment.
Type in your Change notes(Be descriptive, as this will tell you what the change was supposed to be for later, if you need to review your change history in the branch) and ensure you only have the changed/new files you want as part of this commit.
Once you're happy with the note and selected files, click OK. You'll see a pop-up window as it processes the changes. Once it's done, the changes are stored!