I'm sure GCHQ will explain this far better but my understanding of the goodwill charge is something along the lines of the club actually being physically worth something in the region of £xmillion (say £500million) in terms of physical assets when the Glazers bought it but they actually paid something in the region of £800million for the club (the amount it cost them to buy up all the shares).
This surplus is what makes up the "goodwill amortisation". It has already been paid but gets spread over 15 years or something on the accounts. Something like that anyway.
Yup, that's pretty much it. When the Glazers purchased the club for £790m, the ''fair value'' of the club's identifiable net assets was stated as c. £260m, which is how the c. £530m of goodwill arose. That £530m essentially reflects what the Glazers paid for the club's brand value and its future earnings potential (although in reality I'd argue that the club's net identifiable assets were undervalued by c. £100m).