How do you use the backpack?

basically, your backpack is the same in every project. this means if you drag some code, a sprite, a costume, or a sound into the backpack in one project, it'll still be there if you're in another project, and you can take it out.
this makes it easy to bring stuff from one project into another.

To use the backpack in Scratch, just drag and drop sprites, sounds, or costumes into the backpack area at the bottom of the project editor. This saves them for later use. When you want to use them again, open the backpack and drag the items back into your project.

Here's the video to - https://www.youtube.com/watch?v=AuolBPY8qdc

@ametrine_ and @82bitmystery thank you.