Docker works same as virtual machine. But its surprisingly fast since it use host OS for computation rather running as complete separate virtual machine.
To learn docker, first you need to learn basics about docker architecture and docker life cycle. There are lots of materiel out there to learn it. Apart from that, you can follow interactive tutorials such as Katacoda to practically try out. It's really help me to learn both Docker and K8s. They have lot's of tutorials available to learn Docker and you can also contribute to create tutorials.