Broadband DSL PPP PPPoE IpoE

Studying ISP broadband/DSL technology. Can someone explain what PPPoE is and why it's used? I'm interested in the 'ethernet' side of things, the broadcast part - does it allow more single devices in a home/business to connect or does it provide a lan to an area/street? What's the benefit in simple terms? Also, how is it put over copper telephone wire from home to the exchange, the local loop? Any 'idiots' guides welcome.

Try this http://lmgtfy.com/?q=what+PPPoE+is+and+why+it%27s+used

PPP over e for vdsl or a for adsl is a bt wholesale choice. Other LLU providers like sky don't use ppp.
As used by BTW it's only intended to be one device per line.
It's nothing to do with any sort of local area access.
How it's put over the wire (or maybe fibre) is very complicated at the detailed level of how *dsl or gpon works - but less complicated thinking (for vdsl) of eth frames go in one end and come out of the other
A pppoe frame is just an ethernet frame with it's own ethertype the ppp header is in the payload leaving 8 bytes less for the (usually) IP packet.
The broadcast part - I don't know the detail of how openreach do things at that level. It's possibly along the lines of TR 101 (search for it, also there are BT sins easily available that have other info in them).