There are three types of referencing in Microsoft Excel
Relative Reference- Basically when you write a formula, say "=B2+A2" in cell C2 and have numbers present in the B and A column and you drag the formula in column C. You get formulas corresponding to column "B" and "C". As in this case you get "=B3+A3" in C3, "=B4+A4" in C4 and so on.
Absolute Referencing- This referencing is used to assign a fixed value and to not change with respect to changing rows and columns. In this case, suppose we fix dollar signs just before the address of the cell, it won't get changed when you drag it.
For example- "$A$2" means that now the value in cell A2 will be used for all formulas.
Mixed Referencing- This type of referencing help us to either fix rows and change the value by varying column or fix columns and change the value by varying row. This is used by putting "$" dollar sign just before the column or row address. For example- If the formula is written a "$A2" then the column is fixed while the number 2 will vary when you drag it.
As seen in the example, the column would have remained the same either way.