Amazon Cloud is the place where you can create a number of ec2 instances in a Virtual Private Cloud.
You can get the complete documentation in the link http://docs.aws.amazon.com/AmazonVPC/latest/GettingStartedGuide/ExerciseOverview.html.
Here I am listing some commands usefull to check varrious things in an amazon instance
Once you launched an ec2 instance in an VPC , there will be a default path where amazon API tools are located. The default path on my instances are is /opt/amazon/api-tool/bin/
1) How to check if an elastic ip is attached on the machine or not
It will list the elastic ip on the amazon
2)To list the instance information of all machines on the amazon
ec2-describe-instances -K ~/.ec2/*.key -C ~/.ec2/*.crt
it need amazon keys to work