I cannot create a team.

Whether or not team-up function is enabled depends on the competition type. When it comes to the competition where the function is enabled, you can see the Team Up button appearing next to the Submit button. Note those one of the following conditions applies are not allowed to join a team when:

The user has already teamed up.
The user already belongs to another team.
The user whose“individual participation”has been confirmed.
Please note that if you submit individually even once before forming a team, your “individual participation” will be confirmed.

Also, users who fall under the following category cannot be invited to a team:

The user who already belongs to another team.

Teams are specific to each competition. If you're joining multiple competitions, you'll need to create a new team for each one.