In algebraic notation, you must specify either the file or rank of the specific piece you'd like to move if an identical piece can also move there.
in the following image, there's a knight on c6 and another knight on e2. There's an arrow going from the f2 knight pointing to the d4 square.
if you'd like to specify this move, then you'd write
- N2d4 or
In some rare cases you must name both file AND rank. This usually happens when there are 3 of the same pieces on the board, in most cases; 3 queens.
In the following image there are 3 queens, one on d3, another on d7, and another on f7. There's an arrow going from the d7 queen pointing to the f5 square.
this move would be:
The "Q" before "d7f5" is redundant because only a single piece can possibly be on the d7 square so you can just leave it out.