There have been times when I opened browser windows and applications on my iPhone and felt like taking screenshots from it either because I was testing some Mobile application or assisting my mate in developing some website. 
It is probably too late to tell people how to take screenshots from the iPhone; however I believe there are people like me who prefer exploring things on their own instead of just typing few key words and find it on Internet. I mean, don’t you think that it gives a sense of achievement when you explore something on your own? Remember those days when you were able to solve those mathematical problems without assistance and it filled you with a sense of pride? It did to me.
Anyways, first thing first. Last week I mistakenly pressed the top menu button and the round menu buttons together and it took a screenshot of the current screen. It actually took me few moments to understand & realize what had happened. But finally I knew what to do when I needed a screenshot of my iPhone.