I'd suggest to read "Kubernetes: Up and Running" book, it's short enough and cover basics of k8s. Also it's important to have hands-on k8s cluster, so Google Kubernetes Engine would help a lot about spinning up a cluster.
I had to get up to speed on k8s at work this year and from that experience I would recommend to use minikube at first. Only go to GKE or such once you outgrow minikube. Doing minikube first also makes for a nice way to develop an application. Minikube for local development and testing, then deploy to GKE for QA & prod.