Back Titration question

[Henreezy]

I'm trying to piece together back titration but the way the book explains it seems very shallow to me.
I don't understand the concept very well at all, could someone give me an elaborate explanation as to what is going on using this question as an example

[Shenz0r]

I shall quote myself from around a year ago, hopefully this analogy works for you.

Suppose that you're having a birthday party, you invite your friends, and you order a box of pizza (your initial amount of mol of the standard solution), which has eight slices of pizza. You and your friends start to eat the pizza. Then, you find out that two slices of pizza are remaining (which is how many mols of the standard solution is in excess). If you knew that one person could only eat one slice of pizza each (the molar ratio), then you can easily deduce that six slices were eaten and so six people must have been at the party (the amount of mol of your unknown substance). Hope that makes sense.

Work out the original number of mol of the standard solution, then work out the excess number of mol of it from your second titration. Remember that n(reacted) = n(initial) - n(excess), and then you'll have the number of mol of the standard solution that reacted with your unknown solution (you'll find out how much pizza was eaten at the party, and then how many people there were).

[Henreezy]

Alright, I'm pretty sure that clarified the process for me, now time to do some questions!
Thanks Shenz0r :^)