Re: general flyfishing question...
Generally you are going to let your fly drift with the current. That's what natural insects do and that's what the fish will be looking for. Look for the seams where fast water meets slow water and cast upstream along those seams. Strip in slackline as the fly drifts back to you. I'm simplifying things a bit here but it's a good place to start.
Your best bet would be to get an experienced angler to go fishing with you. He or she could shorten your learning curve quite a bit. Good luck!