How do you use an ATTINY? what can it do?

This video is a start:- How-To: Shrinkify Your Arduino Projects - YouTube

This is what I made with mine. A drum that echos back what you tap. It was designed for an autistic kid who liked the feel of the buzz when he hugged it. The Neopixel LEDs change colour for each tap it plays back so you can use it to teach counting as well.