I do realise that you chaps are indulging me here, and that understanding all this is of no use whatsoever to an ageing trolley tart. It's just that I've always been more interested in technical stuff than in reading the Hello!
- always happy to 'indulge a 'trolley tart'
Point 1) You missed the rest of the quote off -
or 'pressurised' by using the APU compressor to provide an air supply.
- does that clarify?
Point 2) Not sure what you mean.
Point 3) Yes
Point 4) The 'bleed air' - from whichever source - is used to supply air at a higher pressure to various things, including,
in this case, the air conditioning packs.