Currently, New Scratchers cannot create studios. In order to create a studio, you'll need to reach Scratcher status on your account.
To become a Scratcher, you must be active on Scratch for a while, share several projects, and comment constructively in the community. After a few weeks, you will receive a notification inviting you to become a Scratcher. If you accidentally close this notification, that’s okay! Look for the link at the top of your profile page (next to your username) to become a Scratcher.