Like @kasie said, the best thing to do is follow the book that came with your deck!
Other than that, you have to use your intuition!
There is no system for Oracle cards like there is for Tarot cards. Oracle decks are all different: They can have any number of cards, different uses and ways to use them, depending on the deck.
However you can use Tarot spreads with Oracle cards as a starting point.
My first deck was an Oracle deck (Oracolo dello sciamano) and I still use it. I tend to just draw one card per question because that’s how I did it before I learned any spreads.
Oracle cards generally have a word or sentence added to them that you can use to help interpret the card, but you don’t have to.