There are allot of paid applications out there that will record what you are doing on your iPhone for a price; for things like presentations or "How To" videos.
I am going to show you in this video how you can do it for free; if you own a Mac computer.
So go ahead and connect your USB cable to the back of you Mac, and follow along.
Once you are done, the file will be formatted as an .mov, which can get rather large, and not too useful for web content.
To export it to something more manageable, go back up to File -> Export - > iPhone, iPad
It will give you three options with the size of each option underneath. This will save the file as .M4V which will have better compression.
Let us know if you have any questions in the comment box below.