The best way to know how to do calculations and report your answers to the correct number of significant figures is to practice! In here there are a few opportunities to check your understanding of this concept.
Try all of the general chemistry practice problems: http://bit.ly/ProfDaveGCPP
General Chemistry Tutorials: http://bit.ly/ProfDaveGenChem
Check out "Is This Wi-Fi Organic?", my book on disarming pseudoscience!
Barnes and Noble: https://bit.ly/3pUjmrn
Book Depository: http://bit.ly/3aOVDlT