There will be times you will need to know how to do this if you are asking for help, and it is quite simple.

We should all have msn Paint on our computers and this basic program will open your screenshot. Some of the other graphics software may also work.

1) When you have the screen up that you want to copy, press the  "Print Scrn" key (usually located on the top right side of the keyboard

2) Open your Paint program

3) Right click in the work area and select "Paste" Or Ctrl and 'V' and your screenshot will appear

4) Click on File > Save as

5) Type in a title.  In the drop down menu for the file format, select .jpeg, .jpg, or .gif.  (Paint normally defaults to saving pictures as bitmaps and those file types are generally a lot larger than others.)  If you find you do not have any other save options (other than bitmap) clean out cookies and temporary internet files and try again.

Bitmap is OK but it can make things a bit blurry.

You can choose to Edit your screenshot if you like and cut out the bits you don't require.