if your sheet looks something like below where there are multiple names in different rows, then the easiest way is the autofilter function. once you have filtered the names you want you can just highlight the name in one column, and on the bottom right of xcel there should be a "count=4" or something to count how many names you have.

A B
mike jones
paul smith
stan walter
me you
mike jones
paul smith
stan walter
me you
mike jones
paul smith
stan walter
me you
mike jones
paul smith
stan walter
me you

Flitered Information

mike jones
mike jones
mike jones
mike jones