What formula would I use if my first column have
"Calicdan, Prince Russell"
"Fabro, Aiza"

and on my second column I want it to display with a format like firstname.lastname. so result should look like these on the second column:
"prince.calicdan"


"fabro.aiza"

this will work, but it's not clear for me what you want, because on the first name, you remove third name and you switch places between the two names left... And , on the next row, it is a different situation. You want a different formula for every row??
Try: (works on second row, for the first row you have to be more explicit)
=LOWER(LEFT(B4;FIND(",";B4;1)-1))&"."&LOWER(RIGHT(B4;LEN(B4)-FIND(",";B4;1)-1))