I am assuming that you are asking with respect to Windows. The supporting screenshots are from Windows 10.

• Search for Snipping Tools in Programs

• Snipping tools will thus open.

• There are four options in Mode: Free Form snip, Rectangular snip, Window snip and Full Screen snip.
• When in Free form or Rectangular mode, click New to take the snap of the required part of the screen.
• When in Window mode, you will be asked for the required window whose snap you want to take.
• When in Full Screen mode, the snap of entire desktop will be taken.
• Using Delay option you can delay the timer according to your needs.

  Hope this helps.