Mac
To make a screen on a Mac, you have three different options:
Whichever method you use, your screenshot will be saved to your desktop.
PC
Taking a screenshot on a PC is a more complex problem depending on which version of Windows your machine has installed.
For a PC running Windows 8 or better
To capture a screenshot and save it as a file, press the Windows logo key +PrtScn. The screen will dim for a moment when the screen is copied and saved as a file in the Screenshots folder (which is in your Pictures folder).
To capture a particular screen, tap or click the window you want to capture. Press Alt+PrtScn to copy the window into memory. You can paste it wherever you like.
For a PC running Windows 7 or Vista
Press PrtScn to copy the window into memory. Open Photoshop, or any image editor of your choice and start a new file. Paste the screen shot into the new file. Edit and save.
IOS
Press the Home button and the Sleep/Wake button simultaneously. Your screen will flash white. Your screenshot will be captured and saved to your Photos app.
Android
Press the Volume Down button and the Power button together and hold for one to two seconds. Your screen will flash white and capture the entire screen. If that doesn't work, try pressing and holding the Home and the Power buttons. Your screenshot will be saved to your Gallery or Photos app.