iBooks and disappearing toolbar iPhone

Hi
Ive been getting used to using iBooks for reading an eBook I downloaded. I find the toolbar (with the bookmark icon and other icons) disappears sometimes. I dont know how Im causing it. I try tapping the screen a few times and it comes back again.
How do I make sure the toolbar stays shown all the time? Is there an online page that shows how to use iBooks properly?
Thanks
15 inch MBP 2.4GHz Core 2 Duo Mac OS X (10.6.7) iPhone 4 iOS4.2, Apple TV 2nd Gen, iPod Nano 5th gen, iPod Nano 4th gen