Copying permission levels will make them available on the target site to assign permissions to users and groups. You can access a complete breakdown of the SharePoint permission levels on Microsoft's permission level library.
Index
Prerequisites
You have site collection admin permissions on your source and destination site collections.
Note: Site collection admin permissions are required even if you have higher admin privileges like SharePoint admin or global admin permissions. For more information, see Microsoft administrative permissions.
How-to
Select Copy from the menu.
Select Copy structure and content.
Click Connect.
Select your source.
Click Next.
Click Connect.
Select your destination.
Click Next.
Select Permission levels from the list of Site objects.
Select the permission level(s) you want to copy from the source.
Drag and drop them into the destination, or click Start copy on the bottom-right corner.
Once the action is completed, the migration report will show any successes, warnings, or errors. See Migration Report for more details.
Note: If you select Manual Operation Mode in Options, you will be prompted to select between Merge and Skip when you copy a permission level that already exists at the destination site. If you select the option to Merge, the rights associated with the destination permission level will be overwritten by the rights associated with the source permission level.