1. Press the "Print Screen / SysRq" button on your keyboard while viewing the page you want to take a screenshot of.

2. Press "paste" (Usually Edit > Paste) in a program that supports images (eg. Micrsoft word, Paint Shop Pro, Paint, etc.) The screen you took a screenshot of should appear.

3. Crop, edit and do whatever you want to the image then save it. I would not recommend saving it as a JPEG image since it causes it to slightly blur. For a screenshot with not too many colours, GIF would be a good file type to use. However, saving it as PNG will give it the best quality, although it will have a slightly bigger file size. Saving it as BMP will just cause it to have a massive file size, so I don't recommend saving it as that.