There is an official website and there are multiple ways to learn CloudFormation. Just curious what worked best for you.
Linux Academy has many great courses on CloudFormation as well as other AWS and DevOps tools and services. They also have many guided labs where you will be given hands on guided learning of how to use various technologies.
Otherwise, creating templates and launching CloudFormation stacks is something that you could learn by just creating infrastructure piece by piece in your CloudFormation template (ex. add an S3 bucket to your CFT -> launch stack -> add and EC2 instance -> launch stack -> etc. etc.). The AWS documentation is very helpful along with a good plugin for your IDE.