When you want to find the row or column number of a cell, you use ROW() and COLUMN() functions.

If you don't write anything in paranthesis, you get the order of row or column of the cell where the formula is written.

If you write a cell name in formulas, you will get the order of row or column of the cell which the formula refers.

Whereas " =ROW() " function gives the row number of B20, " =ROW(C10) " gives the row number of C10 without regarding where the formula is written.