How to take a screenshot
You can take a screenshot on your iOS devices including iPhone. Screenshots are very useful. For example, instead of taking a brief note of some information, you can take a screenshot of the information and keep it in your iPhone.
Press Home button and Sleep/Wake button at the same time
To take a screenshot on your iPhone, make sure that the image you want to capture is showing on the screen. Then, all you have to do is to press the Home button and the Sleep/Wake button at the same time.
The screen capture will be stored in your "Photos" app.
It is rarely the case but still sometimes you can't take a screenshot of iPhone's display in a certain situation. For example, when you try to capture the screen while on a phone call, the call will be disconnected. Also, you can't take a screenshot of the "slide to power off" screen to turn off your device.
In such cases, it is recommended that you use mirroring software such as AirServer, which allows you to mirror your iPhone's screen to your computer. So, with this software, you only have to take a screenshot of what's on your computer display. Though there is a less likely chance that you will need a screenshot that cannot be taken on your iPhone, try those kind of software when you really want such a screenshot.