If something is loose, it's not attached very securely to anything. Be sure the horse trailer attached to your truck isn't loose, or it might just roll away on its own while you're on the highway.
Loose means "not fixed." We can use it for things that you physically attach, like doorknobs or buttons, or for ideas that aren't rigid. If someone has loose morals, they don't have a strong moral code. A floppy dancer has loose limbs, and a loose ball is one that no one's holding. It's also a verb. To loose something is to set it free, which is different from losing it. You loose the wild squirrel you nursed back to health.