As a previous contributor said, they are not examined now under JAA, but I had the misfortune of doing both under the CAA exams.
A Perfrmance A aircraft is goinh to be an airliner - tuboprop or jet. The exam was based on a jet and a Perf A is always safe.
A Perf A aircraft, if it has an engine failure during take off, will either be able to stop on the remaining runway or safely accelerate to take off speed and climb clear of all obstacles.
You had to work out max take off weights, or given a max take off weight, claculate max take off temperature or V speeds etc from many many many graphs using a very thin pencil.
I believe more information may be found in JAR OPS 1 Subpart G.
A Perf C is a light twin, something like a Seneca 2 or a Chieftan. It will fly on one engine but it might well scare you with its (lack) of climb rate. When I flew a Seneca, our Ops manual said that it would take about 20miles to climb to 1500'AAL on one engine at MTOW - not very nice!