At first you'll simply calculate which atom on a polyatomic ion carries charge. But as you get into more advanced reactions you'll be using formal charge to identify reactive intermediates and reaction patterns.
The standard formal charge formula covered in your text is lengthy and confusing. This video shows you my formal charge shortcut which takes just a few seconds once you get it.
(Watch on YouTube: Formal Charge. Click cc on bottom right for video transcription.)
This is Video 4 in the Orgo Basics Video Series. Click HERE for the entire series.
Don’t miss the Written Tutorial Formal Charge Formula and Shortcut for Organic Chemistry that is also apart of the Orgo Basics Series.