bike rack

I always see some of the cars having a bike rack for suvs on top of the roof or behind their cars. Before, I was wondering about it then I found out that they were there for the bicycles. I think it is nice to be a rider, but I do not know how to ride bicycles. I did practiced riding a bike before, but I got nervous so I stopped. I ride bicycles sometimes at the gym, the spin bike. So funny, but how I wish I can ride the real one.