Total Times for amount of work someone did.

I'm sorry if this doesn't make sense and that I can't attach any document because I only have MS Office on another work pc that blocks forums. I will try to best describe what I have so far.
Column A: Start time.
Column B: Stop time.
Column C: =(B-A) giving me a total time in hours, minutes and seconds.
So far this works like a charm. Now for the formula I am stuck on.
Basically Column D is someones name (whoever worked on that time total and they are just typed in as they are assigned).
What I want to do is, on worksheet 2 or off to the side of worksheet 1, have the total amount of time (hours:minutes:seconds) that, that person was assigned throughout the entire document.
So basically if John does 20 minutes in row 3, 20 minutes in row 20, and 20 minutes in row 50; I will have a table or something showing John did 1 hour total in the document (while auto adding all of this up).
If someone could just tell me the function to use or has any advice I would greatly appreciate the help. Again, sorry if this is a confusing description and if you have any questions please let me know and I'll try to explain it further. Thank you.

Try the SUMIF function.