A screenshot is an image copy of what you see on your computer screen. A screenshot can be captured from basically anything you are looking at. Examples include web pages, pictures, open programs or documents such as MS Word, PDF files, or literally anything you can see on your computer's monitor. Screenshots are taken manually by pressing the Windows print screen key on your keyboard which saves the image to your computer's clipboard.
In the example below I am taking a screenshot of a public domain image of a map from a web page. I want to e-mail someone an image of the Channel Islands south of Los Angeles California.
STEP 1 - Locate the source that you want to take a screenshot of. In my case, I want to take a screenshot of a map on a web page that shows the islands. I found a suitable map on wikipedia that shows the islands and is a public domain image.
STEP 2 - While viewing the web page (press F11 for full screen mode - or scroll to the exact region you want) I pressed the Print Screen key.
Note: Pressing the PrtScn key won't appear to make anything magically happen. It simply saves the screenshot image behind the scenes. STEP 4 is where stuff happens.
STEP 3 - I then click on Windows Start > Programs > Accessories > Paint
STEP 4 - Once Windows Paint is open I then paste the image by pressing the keyboard keys (Ctrl + V). By doing this the screenshot is then pasted into Paint like the example below:
STEP 5 - Inside Paint the image can be moved around manually. I have used Paint's Rectangle Tool to not only move the image but also to select the specific region I will output as a final. Paint's Edit > Copy To options will save the selected region as a BMP file to the desktop. This can later be opened inside Paint to change it from BMP to GIF or another more usable image format. See examples below:
The selected screenshot region in Paint.