Taking a screenshot on an Android phone is typically possible by holding down the power button and the volume down button at the same time. This is tricky to do; and saving or sharing the screenshot requires too many hoops to jump through.
A solution that I found is a small app called “Selection – Screenshot & Crop”. Once the app is launched and enabled, you simply go to the notification area of the phone (at the top) to initiate the capture sequence. Once initiated, a grid will appear on the screen that will allow you to crop your selection; then, you can subsequently share the screenshot through other apps (such as your email). I have tried many screenshot apps and this one is the simplest I have found to use and is now a keeper on my phone.
SOURCE: Google Play – Selection – Screenshot & Crop (to install on your Android Smartphone, open the Google Play app on your phone and search for “Selection – Screenshot & Crop”)