Greenshot is a very similar to the snipping tool that comes native with Microsoft. We install it over the snipping tools since it has some extra features we find useful.
Pressing the PrtScn (print screen) button on your keyboard or laptop will cause a cross hair to pop up and then allow you to "snip" a section or full screen to screenshot.
When the screenshot completes a drop down menu appears to let you have options of what you'd like to do with your screenshot. You can edit it in their editor to add things like arrows and boxes, copy it directly to whatever you need it to, or save it etc.
NOTE: On Windows 11 the PrtScn button has been defaulted to Snipping Tool even with Greenshot installed. If you go to your start menu and typing "accessibility keyboard" and click on the top option you'll get a new menu pop up. Scroll down and turn off "Use the Print screen key to open snipping tool"
This will make Greenshot your primary screenshot tool instead, just like we did on windows 10. You'll just have to reboot one time after you turn that off and it'll be set.