I would suggest the Amazon Docs for the AMI Tools. They detail the steps for various approaches, including using a command line.
The basic steps you will go through are:
- Setup the command line tools
- Choose your AMI (ec2-describe-images)
- Setup your key pair (and setup PuTTY so you can SSH into the instance, you can import your key with ec2-import-keypair)
- Setup your security group (the default group is called 'default'; use ec2-authorize to open ports)
- Start the instance (ec2-run-instances)
If you are just starting with EC2, I might suggest using the AWS console (web interface) to simplify some of the above tasks - you will still need PuTTY and a key to do anything meaningful though.