First install the Python package:
apt-get install python python-pip
Then issue the AWS CLI Installation:
pip install awscli
If all went ok, you should be able to execute for example
which will help you to create an initial configuration file containing your credentials, region and output format.
For more help type:
Or for EC2 specific options:
aws ec2 help
For S3 specific options:
aws s3 help
The documentation can be found here.