Copying the image from your screen can be done by using the Print Screen key on the keyboard and you can then paste the screen image into a document.
However if you just want a small part of the screen to be copied, you can use Snippy. Snippy is a small programme which youc an save to your computer. By clicking on the snippy icon in the toolbar you start the programme which enables you to draw with your mouse around the section of the screen you want to copy. This is copied to the clipboard and can be pasted into a document.