If you work with more than one note type, you'll end up switching between several templates. Instead of copying each one out of Anki again every time, you can save a template you're working on inside the editor and pull it back out later.
Click [My Templates] at the bottom of the editor to open the library. Type a name (like "English vocab" or "Japanese example sentences") into the Template name box and click [Save Current Template] — that's it. The Front Template, Back Template, and Styling you're currently editing get saved together, sample values included. Saving under a name that's already used will ask if you want to overwrite it.
Click [Load] next to any saved entry to switch to it. Since that replaces whatever you're currently working on, you'll get a confirmation prompt first. Clean up templates you no longer need with [Delete].
A good habit is saving a checkpoint before a big change. If you're experimenting with colors or layout and it isn't working out, you can load the saved version and get back to where you started.
One important thing to remember — My Templates is stored only in the browser you're currently using (via localStorage). It won't show up on a different computer or a different browser, and clearing your browser data deletes it too. For anything you want to keep long-term, use [Copy Code] to copy the code out and save it somewhere else, like a text file.