How to concatenate or join columns value in excel

Sometimes there is a need to join or concatenate columns value that comes from different column. And of course to make the joined value most often we use underscore to identify the value comes from different columns

For example 

Cell A1 = Bobby

Cell B1 = Mark

Let say you want to concatenate Bobby and Mark name using underscore from Cell A1 and B1. Simply use the following command;

=A1,"_",B1 Or

=Concatenate(A1,"_",B1)

The result yields = Bobby_Mark