A quick Google search with the terms
Xen Tutorial returned the
How-Tos section of the Xen Wiki and an
article at Linux Journal. I'm sure with more than 2 minutes of searching you'll find more.
The difference between para-virtualization and full virtualization is that the latter simulates
every piece of hardware the guest sees (CPU/Disk/Memory/NIC/...). With para-virtualization, however, the guest knows that it's not the only OS on the iron, and can request resources from the host kernel, instead of having to go through additional software layers.