The dollar sign restricts the column, row or both depending on where you put it.
For example:
1) $A1
2) A$1
3) $A$1
All do different things. 1 keeps the 'A' unchanging when you drag the formula down, 2 keeps '1' unchanging and 3 keeps the exact cell reference unchanging.
This thread made me chuckle. I am working at an investment banking job for the summer so all my days are spent with data entry in Excel. I learned so many excel functions that I didn't know existed before. 😀