You can take a screenshot using your iOS device.
If you use an iPhone X, scroll down for more instructions.
Press the Power and Home buttons.
On iPhone 6 and later the Power button is on the right side of the phone. Earlier devices have the Power button at the top.
Your screenshot can be found in the Screenshots album in the Photos app.
After taking the screenshot, a thumbnail of the screenshot will appear. Tap on the thumbnail to open a screen where you can annotate your screenshot.