What does each permission level mean?

Answer

Although there are differences between what users can do in each tool, the common differences between the permission levels are as follows:

None. Users have no access permission to the tool.
Read Only. Users have view-only access permission to the tool, but no editing permission (Note: The granular permissions feature in Procore permits you to assign a limited number of task-based permissions to Read Only users to address special use cases. For details, see Can I provide users with 'Read-Only' level permission with limited access to update information in Procore?).
Standard. Users have limited access permission to the tool. They can create items, and assign items to other user's who have 'Admin' level permission to the tool. They can also be assigned to respond to items that require them to perform further actions in the tool. In addition, 'Standard' users can be granted granular permissions. See Grant Granular Permissions in a Project Permissions Template.
Admin. Users have full authority to use all functions of the tool, including configuration capabilities.