okay, here goes:

Step one:

Highlight the cells, right click, and hit "format cells"

Select type, and from the list select time. It will give you a number of time formats. The easiest ones to work with for time clock functions are 24 hour times, but it's up to you.

if A1 is your start time, and B1 is your end time, then c1 will be =b1-a1.

to total the times in column C, at the bottom type in =SUM(C2:C10), and it will total your time in hours and minutes.