As Borek stated Thomas,
When you are looking at your buret, and you fill it to the top (Oml mark) and begin adding it to the solution, you stop once you have reached the yellow color in solution.
Initially you were at 0ml of HCl added.
Finally you were at X(whatever) number of ml added.
When you subtract the final - initial = net amount added (simply looking at the buret would tell you how much you added though if you started at 0ml)
Then apparently you had to do this 5 times, each with the same calculation as above.