So I understand how when creating a group rank, you can make permissions for each seperate dscission, but how would I make it so a group has the same permissions for every single discussion, and every new one to come?

You can select what permissions your group can do in the forum you want.
Please go to

ACP(Admin Control Panel) > General > Forum > Categories and forums >Forum Permissions Control

You only need to mark the permissions in the list that the group have in the forum you have selected.

When creating new forums, you have an option to copy permissions from forums already created.

What about when someone else creates a topic. Can you automatically set it to add those permissions no matter who makes it?

If you set the permissions for the forum, it applies to every group that you set for that forum.