If you are not a system administrator, you cannot create a space by yourself. However, you can enter a request to create a space from the navigation bar or from the Preview.
Click on the "+" in the navigation bar next to "Groups and Spaces" or go to the Preview and click on "Request a new space".
Submit your request by following the various steps provided.
This request will be communicated to the system administrator, who will validate or deny the creation of the space. By default, you will be the administrator of the space.