I know a bit about it. The Orisha overlap with the Catholic Saints.
You also may not want to offer the Orisha blood because once you do, that's what they'll get a taste for from you. Candles and specific foods seem to work just fine: Rum for Elegua. Cigars for Chango, etc.
Each Orisha has its own day and a number and color of candles associated with it.
I know there's a lot more to it than that. I'm just keeping what I say to a minimum so the depth of my ignorance can only be suspected!