Cell referencing formulas is possibly the most important thing in Excel. This first video on them will focus on locking or not locking references and why. Below is the link to the file if you want to use the same Excel book I am.
https://docs.google.com/spreadsheets/d/1cunTJVgFp5sY74FqUfk9f2J2RDn7gQvUU6cH4R9HTiA/edit#gid=1912643724
