You can work with two accounts by creating two profiles on the aws command line.
It will prompt you for your AWS Access Key ID, AWS Secret Access Key and desired region, so have them ready.
Examples:
$ aws configure --profile account1
$ aws configure --profile account2
You can then switch between the accounts by passing the profile on the command.
$ aws dynamodb list-tables --profile account1
$ aws s3 ls --profile account2
Note:
If you name the profile to be default it will become default profile i.e. when no --profile param in the command.
More on default profile
If you spend more time using account1, you can make it the default by setting the AWS_DEFAULT_PROFILE environment variable. When the default environment variable is set, you do not need to specify the profile on each command.
Linux, OS X Example:
$ export AWS_DEFAULT_PROFILE=account1
$ aws dynamodb list-tables
Windows Example:
$ set AWS_DEFAULT_PROFILE=account1
$ aws s3 ls