What different kinds of user types are there?

 Here are the different user types and permissions members of an asset library can have: 

User types: 

Owner: Owners have all the rights listed below as well as the right to assign people with roles and permissions. 
Administrator: As an administrator, you can reach the "Content Administration" page where you upload images, create collections, share collections, invite people, assign roles and permissions. 
User: As a user, you only have access to the public page on the web. There you can download the images in the collections that are published. 
Contributor: A contributor is a user that has been invited to upload and edit specific collections and their content. They will only see the collections they have been invited to.
IT Admin: This user type has the same access as an administrator, but they are also the main contact in charge of integrations and Azure AD connections.

Permissions: 

Billing Rights: The owner of the asset library can choose who has billing rights. If you have the billing rights you have permission to perform actions that result in charges, such as inviting new users, launching image requests and purchasing images from image requests. 
Approval rights: Administrators with approval rights approve uploaded images and created collections generated by an admin without approval rights. If you as an administrator without approval rights have made a collection or have been uploading images, these need to be approved before becoming visible for all users. 

In the Pickit add-ins for PowerPoint, Word and Teams, all users have the same experience regardless of the roles or permissions. It is only on the web where it will affect which role you have been assigned.