Note that you are limited to what you are able to see on the screen view. You can select all of what you see or some of it. You have the choice of a rectangular snip, free form snip, window snip or full screen snip. You select this by selecting the down arrow in the drop down menu next to "New". With the rectangular snip, you are able to snip in a rectangular form what you see on your screen. The free form snip is just that. You can snip whatever shape of your screen view to capture whether it be a triangle, circle, etc. With the window snip you select a window that you have opened that you wish to capture. The full screen snip is just that. What you see on your screen is what is captured.
Once you have captured your screenshot, you can make your own notes and/or highlight selected areas on what you just captured in the captured file. You also have the ability to email your finished product. You also have the ability to save your capture.
The Snipping Tool is a handy tool and can make your computer life a bit easier. Give it a try sometime.