If you don't know what you're doing, DON'T DO IT. Do not interfere with the official photographer. Also, this gets asked about once a week. Best would be for you to try a search on "How to shoot weddings".
As for your bounce card question... anything that's white? If you just google for "DIY bounce card" you'll get loads of results.
As the rest has mention. AD wedding is very important, there is no retake. unless you know what you are doing and confident in doing it. Dont try to shoot it as an experiment shoot. Why not start with pre-wedding first.
For tips just do some google search. The general tips from me.
You must be prepared and your equipment must not fail on that day. Meaning you need to do a checklist beforehand esp battery, card. Lastly be creative and do a recce.