fuck me, this would take some time to give sufficient detail. With the correct hardware its a doddle. Let me try to address the basics;
PAG (Polyalkylene Glycol) (mostly) lubrication oil is compatible with HFC's (HydroFlouroCarbon i think) ie R134a (currently fitted to new EU cars and used since the early 90's) or R1234yf (There are about 10 cars on the road with it, but it becomes EU law next year). There are a huge range of different manufacturers of compressors, and each one recommends there own brand. Denso compressors use ND8 (Nippon Denso formula
for R134a and ND12 for R1234fy. To my knowledge the ND8 is the only oil good enough to be acceptable in other brands, specifically Sanded compressors, which is what we have in our BX's.
Hoses and colours and guages. At a basic level you need three hoses and two guages (you can get away with 2 hoses but its difficult). Red is high pressure (and requires a high pressure guage), Blue is low pressure (and requires a high pressure guage) and yellow is for refrigerant.
Basically you vac down through the low pressure side (which naturally draws the oil upstream of the compressor), then you vac down the high side (they can act as completely different systems), then you refil, by WEIGHT, on the high side. Hmmm, i'll need to edit this later!
To RECHARGE you need a bottle of R134a gas, a waste gas store, a suitable recovery unit, a vac pump, three hoses, a set of guages and a set of very accurate, and expensive scales. At the bare minimum. If you want to do the best job you'll need a TORR guage, gas analyser and some other expensive bits and bobs.
To flush the oil out of the pump you do only need to flush it, under high pressure, with the correct oil, for quite some time. Its not something i'd recommend doing on the bench without some decent equipment.
This should give you enough to start googling. I do have some training docs which i will look to scanning up.