I was making one of my projects and in events is said something about a clone, what is a clone?

Try looking here before asking about a new feature. http://scratch.mit.edu/overview/

A clone is a duplicate of a sprite. Ideally, you can clone as many times as you want (with lag) to create games with multiple enemies, bullets, blocks, drops of water, etc.

you can basically clone 1 sprite (make a copy of it) and tell it to do something in the scripts without making tons of duplicates of your sprite.