you know the little white driges like the one in the pokemon emarold safari zonethat you can only get on your bike with how eggzacly do you get over it

You need the Acro Bike. How to get across is simple, just press the direction you want to go in and B at the same time, that will make you jump. If you want to bunny hop, just press and hold B

Yes. To clarify that (since I had a lot of trouble with it at first too), you tap B and the direction you want to jump at the same time, when navigating the thin white bridges.