So I defeated a demon gate in a province. There were two spoils, one of which was a warriors guild. I can't seem to find it anywhere.Not in the province, not in my hero's inventory, or as a building i can build anywhere. Help?

It unlocks the "warriors guild" building in your stronghold. However, this building's prerequisite is pikemen school. If you already raised all tier 1 unit's buildings, the guild will be unavailable to you on this shard.

Oh I see. Thanks. :) Don't suppose you know how I'm supposed to activate a spider egg I also found? It says I put it in a garrison, but no slots yet. I assume common(the item's rank) is not tier one?

You need a special building in your stronghold to activate it. In the beginning of campaign, before you unlock it, you can sell eggs. Or keep them in treasury as your personal collection of rare stuff ;)

What special building? I assume by you saying in the "beginning of campaign" you mean I will not have access to it for a while? Maybe after conquering a few shards?

Trappers guild. You need to conquer a shard with such a building.

Oh ok. Thanks. One more question, I found some land that is owned by centaurs. To create an alliance I need to kill 5 ogres, but I'm not informed where these ogres are. There is an exclamation point now in the province with the centaurs, but if I move into that province they same dialogue for attack, retreat, or negotiate appears. Could you tell me where to find the ogres?

Somewhere on the map :) Look for locations with "Giants" guard. You can use province list ("P" hotkey) to quick overlook all the sites in your domain.
If there is no such locations - you may explore a bit. Or just crush horse-footers for their impossible quest :)
BTW, I beg your pardon for my awful English.

Thanks much for your help. And your english is fine. :) Ty again.

This quest (and other quests like this) doesn't refer to any specific place, you just need to kill 5 ogres anywhere you can find them :) The exclamation mark only means the place where you need to go after completing the quest.

Edit: Ninja'd :)

Your English is excellent. Don't worry. I think we all are glad that you are here answering questions.

Oh and You are much more polite than the Gremlin Zarrr (your Picture/Avatar) in the game. That's very strange.

This is because my poor knowledge of English does not allow me to show all my sarcasm and acrimony %D
Polite google translator, not me :)

Let me quote "your" game for a moment:

a) UNACCEPTABLE!
b) I see.
:-)

Are buildings received in this manner permanent (i.e. can you use them on different shards)? I've found a few buildings as loot, but it seems like they are all just early copies of the reward buildings for clearing the shard. Can you find buildings in this manner that were not advertised on the shard selection screen, or are the buildings that you find just early access to rewards that you would have otherwise gotten?

Yes.

Exactly.