It's not a difficult task to take a screenshot on Xiaomi Redmi 2. The only thing you have to do is follow any of the below given methods:
Method via Notification tray:
Go to the screen you want to capture, pull down the Notification tray you will find a button showing the screenshot icon. Click on the button and that's it, the screen below the Notification tray will be captured.
By volume and power buttons:
It's a bit easier than the first method, the only thing you have to do is to press the volume and power buttons together and the screen will be captured at an instant.