Question: what is the difference between usb a and usb 3?
Answer: You are mixing up things here. USB 3.0 SuperSpeed (aka 3.1/3.2 Gen1) is just a specification which targets transfer speeds of 5 Gbit/s (625 MB/s) while USB A is a connector: Cables which support the USB 3.0 will have blue plastic inside USB A connector compared to USB 2.0 connectors which are usually white.