Sailfish OS supports a handy way of capturing pictures from the device display.
Press the Volume Up and Volume Down keys down at the same time, and keep them pressed for a second or two until you hear the camera shutter tone and/or see a notification banner appear at the top of the screen with text "Screenshot captured".
The pictures are saved to folder Pictures > Screenshots. They can be viewed in category Screenshots of the Gallery app.
Another option is to install Screenshot app from Jolla Store. This app allows you to take screenshots with a delay of 3 to 15 seconds.
This app saves the pictures to folder Pictures > screenshots (note the lower case s as a difference to the other tool).
Sailfish OS does not support capturing video clips.