Can't find the manual and I don't know what keys should be used together or alone...and so on
Thanks for any help
Two options: one is to hold the power and home button simultaneously until you hear the shutter sound and see a brief flash of the screen. The other option is to go to Settings > Motions and Gestures and enable Palm Swipe to Capture; then you can tilt your hand onto its side (with your thumb away from the screen) and swipe it across the screen to take a screenshot.
Here's a link to the manual:
https://ss7.vzw.com/is/content/VerizonWireless/Devices/Samsung/Galaxy%20S6/GalaxyS6_UM_33015.pdf
