I created my own sprite and would like to save it, so I can use it on different projects, how do I do this?

Right click the sprite and choose Save to local file.

Use the backpack feature. If you click on the arrow next to the word backpack at the bottom of the editor, the backpack should pop up.you can drag costumes, sprites, scripts, and backdrops to the the backpack, and they will be accessible between projects. To use something in the backpack, drag items to their appropriate places (put the costumes in the costumes list, scripts in the editor, etc.).

Happy Scratching!
-Streamline1