Right, this should be my last post on the AV referendum as I fear I'll end up boring people otherwise. This is another video by CGPGrey in which he explains how the Alternative Vote works.
One thing I would add is that AV works by making sure that everyone has one vote in each round of counting. One of the main things people use to argue against it is that AV is unfair people who vote for smaller parties get more of their preferences counted than someone who voted for one of the mainstream candidates. The problem with this argument is that, if you get your preferences counted multiple times, it's because your favourite candidate didn't win. If you only get your first preference counted then that means that (lucky you!) your favourite candidate has remained in the running all the way till the final round of counting.
Another way you could get a system identical to AV would be to have multiple first past the post elections with the lowest ranked candidate eliminated each time and then the people voting again for the remaining candidates until someone got over 50% of the votes. People wouldn't say it's unfair for people who voted for a minor candidate in an early round to be allowed to vote again in subsequent rounds - so why should people claim it's unfair that that happens under AV?