1. Step Start Darksiders 2
2. Step Press Shift + Tab to open the Steam overlay UI
3. Step Click Set Shortcut
4. Step Select a key like Ins as your shortcut to take screenshots
5. Step Return back to Darksiders 2 or whatever Steam game you are playing
6. Step Press the shortcut you defined earlier and Steam will take the screenshot
7. Step When you leave the game, a window will popup where you can upload your screens to Steam or open the disk path where they are stored
If you do NOT want to use Steam to take screenshots, we recommend to download tools like FRAPS that can records videos or capture screenshots quite easily