Step1:
To login into AWS CLI , first need to install AWS CLI package . The CLI package available for different OS .
you can download from amazon website
http://docs.aws.amazon.com/cli/latest/userguide/installing.html
Step2:
Create IAM User account with access key and Secret Key . Dont forget to save , you can not view or download it again.
You can create multiple access key for same user.
Step3:
After installation in windows open command prompt.
in cmd go to path C:Program Files\Amazon\AWSCLI
type ” aws configure” and enter the access key

Enter the secret key and region

Enter the default output format : json (or you can choose any other format also, default is json)
Now you are logged into aws cli
