Here are a few VERY basic things to get you started:

To summon permanent minions:

You can set aliases for your minions: alias min1 abcde-fghijk-lmnop-q
Now you can use 'min1' instead of the long true name of the minion in anything that references it.

Here is the dialog with the various Legates in the guild hall

Heres a list of sites with alot of further info on the Nergal Guild:
Marvin's AWESOME Nergal Evolution Tree
Porkzar's Nergal 101
Tazliel's Nergal Info