Naturally, you need Ansible installed on your host system before using this.
You will also need to export AWS_ACCESS_KEY and AWS_SECRET_KEY as environment varibles before running the playbook. These are your AWS access values.
Then run ansible-playbook ec2.yaml -e 'keypair=FOO' where FOO is the name of your AWS keypair.
NOTE: The first part of the play, 'ec2.yaml' will create a new EC2 instance every time it is run. This is the nature of the ec2 module.