Log in to AWS using Access Key ID and Secret Access Key ID

To complement helloV's answer : you can also use the access key and secret key to generate a signed URL to the console. This signed URL will allow to access the console, without being prompted for username and password.

Many AWS customers are using this technique to provide single-sign on for Federated users.

More details are available at : http://docs.aws.amazon.com/STS/latest/UsingSTS/STSMgmtConsole-manualURL.html

Access Key ID and Secret Access Key are for API/CLI/SDK access. For IAM sign-in (dashboard) you need the username and password. When a new IAM user is added, the user gets username, password, access key and secret key, and the IAM URL from the IAM admin.