Preview, the default tool that allows you to open everything from photos to PDF files on your Mac, has more than a few hidden features. You can edit images with Preview, for instance, simply by clicking the toolbox icon. Preview can also take screenshots. Create screenshots on Mac Using Preview
To do so, open Preview and head to the menubar. Then, click File and select Take Screenshot from the resulting drop-down menu.
Preview opens the screenshot, lets you make a few edits, and save the file wherever you like. If that matters to you, Preview is a solid choice.