For iOS: 
1.Press the Power and Home buttons at the same time. 
2.Hold them for a while and let go. 
3.Open your Camera Roll photos, which is where screenshots are automatically saved. 

For Android: 
1.Press the Power and Home buttons at the same time. 
2.Hold them for a while and let go. 
3.Open your Photo Gallery, which is where screenshots are automatically saved.