azure permission to create "service principal"
Note: The roles of the subscription and the roles of Azure Active directory are different.
Im only owner of my organization subscription in Azure and I need to create service principals.
You can follow this document: https://docs.microsoft.com/en-us/azure/active-directory/develop/howto-create-service-principal-portal
How can I give permission to my user? Or can I create a new role to assign this permission?
If I understand your issue correctly, you want to give the user permission to create service principals. If you are the admin of your Azure Active Directory, you can grant the user Application administrator role. Then the user will be able to create service principals. You can refer to this document.