Welcome to the board...
As long as you enter your times in valid Excel Times, it's pretty easy...
Examples of Valid Excel Time Entries
17:30:00
5:30 PM
Then you can use a very basic formula to calculate how many hours were worked..
A1 = Start Time
B1 = End Time
in C1 put formula
=B1-A1
That is your hours worked.
Hope This Helps..