I am relatively new to this so this might be a stupid question but it seems Docker and Kubernetes go hand in hand so do you need Kubernetes to use Docker or is just something that makes things easier?
Short answer: No, you don't need Kubernetes to learn about Docker or containers in general.
In fact, the Docker in Action authors recommend that you learn about containers and Docker first, then move on to learn about container orchestration systems.
Container orchestration systems are tools designed to help people run containerized applications across multiple hosts. Kubernetes, Swarm, and AWS Elastic Container Service are all container orchestrators. Container orchestrators, especially Kubernetes, tend to be complex machines and you'll want a solid foundation in standalone containers first. Docker in Action, 2ed builds this foundation in the first two thirds of the book.
Docker in Action 2ed covers the core concepts of container orchestration such as "Services" and running services modeled in Swarm in the final third of the book. These concepts and exercises should provide useful context when moving to Kubernets or ECS, should you choose to do that.
Will Myers wrote:...do you need Kubernetes to use Docker...
As a respected author just said - no. In fact, you can run docker image locally, on your machine (i.e. laptop), however, usually for production use they run somewhere else. All major cloud service providers have some infrastructure/services where you could run your image, i.e. on fully managed Google Cloud Run platform which is exactly designed for that.