I have lenovo all in one pc, I want to add USB 3.0 Slot? How to do this?

Sorry, but you can't do that. You would need to buy a new computer with a USB 3.0 slot.

Your computer would need an expansion slot in order to add something like this, and all-in-one PCs generally do not have any. They're meant to be self-contained and you only add things externally.

The only way to add USB 3.0 slots to a computer that doesn't have them is with an add-in card, and all-in-one PCs don't have any spaces for those, so it's not possible.

If you have a USB 3.0 slot already, you could try a USB hub that supports 3.0, I suppose.