You can capture any of the following types of snips:

Free-form Snip.  Draw a free-form shape around an object.
Rectangular Snip.  Drag the cursor around an object to form a rectangle.
Window Snip.  Select a window, such as a browser window or dialog box, that you want to capture.
Full-screen Snip.  Capture the entire screen.

After you capture a snip, it’s automatically copied to the Clipboard and the mark-up window. From the mark-up window, you can annotate, copy, save, or share the snip. The following procedures explain how to use the Snipping Tool.

After you capture a snip, click the Save Snip button in the mark-up window.

Saving Your Snip

In the Save As dialog box, enter a name for the snip, you can give it the name of a post you will be using it in.
Choose a location where to save the snip, and then click Save.

 To Share a Snip

 Apple’s App Store and Google Play

 Update 5/19/2019 Now comes screenshot sizing you can use for Apple’s App Store and Google Play.
There are different sizes of screenshots for the different apps and you must upload a set of screenshots for all device types, in researching I found that there is a huge guide at App Store Screenshot Sizes and Guidelines There are guidelines on screenshots for portrait and landscape and by using the proper size of screenshots it can change the analytics of your blog and it would be something you have to experiment with to decide which size works best.