Don't over think it.
Active Directory is basically just a tiered system which allows you to group users and cluster groups of users while dictating their usage policies.
Here is a good intro video to Active Directory (38 minutes long)
The idea of this system is that users can be assigned permissions based on their roles with efficient grouping. AGDLP and AUCDLP are simply methods of assigning permissions.
AGDLP
AUCDLP
en.wikipedia.org/wiki/AGDLP
To put it simply
AGDLP stands for :account, global, domain local, permission
AGUDLP stands for: account, global, universal, domain local, permission
What these strategies do is allow or deny users access and permissions to objects.
With AGDLP accounts are put in global groups and assigned to domain local groups which are applied to permissions associated to an object.
ACCOUNT---> GLOBAL GROUP----> DOMAIN LOCAL GROUP----> PERMISSION TO OBJECT
So with a quick example a printer is an object, your account needs access to the printer, you are then placed in a global group of the people in your office which has access to that printer nested inside a domain local group.
With AGUDLP universal groups are added. The job of a universal group is to exist among all domains allowing global groups to be combined from different domains. Basically universal groups are just group clusters.
An example in this case a printer is an object, your account needs access to the printer, you are then placed in a global group of the people in your office which has access to that printer nested inside universal group and a domain local group. Typically your global group will share the universal group with other people who need the printer but don't exist in the same domain.