NKB, I'm just a beginner, but from what I've learned so far, they're very good for getting in tune with your intuition. Like mentioned above, Tarot cards are for more specific answers. Oracle cards help you find the answers that are already there. At least that's how they have worked for me.
When I bought mine, I was told to keep them on me at all times. I put them in a rune/card bag and keep them with me at my desk, under my pillow and in my purse or pocket. I've been told to talk to them..but I haven't tried that yet. I always do a divining spell before I use them to make sure my reading is clear.
My main purpose for using them is to keep me on the right path, rather than give me answers to tough questions. Like, instead of "who will I marry?" it's "should I go on this date?". Instead of "will I be successful?" it's "am I taking the right steps to reach my goals?".
Hope this helps :)