Try out "R1C1" reference style in Excel.. it's quite enlightening to see how things actually work.

If I have a formula in cell C4 saying "=$A4 * $A$1 + B4", that would translate to a formula in cell R4C3, "=RC1 * R1C1 + RC[-1]".

The relative references are much clearer. If you "fill" a formula it looks the same everywhere.