TO MAKE A SCREENSHOT, FIRST CHOOSE THE WEBPAGE YOU WISH TO CAPTURE. THEN...

...click on Prt Sc (Print Screen) SysRq

You now have copied an image onto your clipboard.

Unload this image by going to IrfanView, PaintShop Pro, Photoshop, Paint or any graphics editor.

Paint is found on every computer: Start > Programs > Accessories > Paint

To make your copied screenshot appear in Paint, go to Edit > Paste

Now you can edit the image.

Image > Stretch/Skew to make it smaller by 50%, for example.

Check the width and height under Image > Attributes

Save the image into your website images folder when you're happy with the size.

Save it as a gif or jpg - NOT as a bmp

To take a detail from a picture, select it - usually with a rectangular tool - and go to Image > Crop. Then save it as a gif (or jpg) with a relevant name