Imagine Cashu like a privacy service for Paypal. You send me some of your Paypal $ to my Paypal Account and you trust me that I won't steal them from you. Great, I like you, too!

After that you can spend those Paypal $ on any online shop that accepts Paypal. The clue: they won't know that it was you who paid. IIRC: Even I won't know.

And: my Paypal Account is not completely private but it has better privacy than any real Paypal account (LN issues...)