Taking a screenshot is not difficult at all:

1. Simultaneously hold down the side button and the volume up button (side button and home button for older iOs devices).
2. Release both buttons quickly.
3. If you have iOS 11 or higher, a thumbnail image will appear in the lower left corner of the screen.

To find a screenshot, go to Photos> Albums and select Screenshots. Attach a screenshot to this dialog using the "+" sign in the bottom corner.