By default on the MacOS, taking a screenshot can be done either by pressing:
CMD + Shift + 4
This option gives you a new cursor that you can drag across the screen to select the area that you want to a take a screenshot of by dragging your mouse across the screen. Once selected the screenshot will pop up in the bottom right hand corner of the screen, you can swipe it away and it will save to the desktop or you can click it to bring up some annotation options and the ability to save it elsewhere.
OR
CMD + Shift + 5
This option gives you a new overlay in which you can have a more detailed screenshot made of a selected area. You can resize the box and drag it around or choose to take a screenshot of the whole screen or just the selected window. Once you click capture you can then use the same annotation options as the previous shortcut.
You can change these shortcuts if they are not to your liking by going into System Preferences/Keyboard then going to the top bar, clicking shortcuts and on the right hand side there is an option for screenshots. Click this and you can change the shortcuts in here.