Usually, you need to run following four commands to create a user.
#!/bin/bash
# create bare user
aws iam create-user --user-name <user> --tags Key=Creator,Value=kasung
# enable aws console access
aws iam create-login-profile --user-name <user> --password <password> --password-reset-required
# create access keys for programmatic access
aws iam create-access-key --user-name <user>
# add user to a group to provide permissions
aws iam add-user-to-group --group-name <group> --user-name <user>
To find what are the existing groups you have, enter following command:
aws iam list-groups
aws iam list-groups-for-user --user-name <existing-user>