you do not need a * in your exams - it would help like in all things but it is not a mandatory requirement. A number of pilots I have known/know have very few qualifications. What you need is an ATPL (airline transport pilots licence) which enables you to fly commercial airliners. This you obtain when you have 1500 flying hours and will take you about 2 years of flying to acheive.
You can start flying passengers on an airliner on an ATPL ( frozen) which means you have passed all the higher level theory exams at ATPL level but do not have sufficient hours yet and are flying on a CPL ( Commercial pilots licence). To get a CPL is what you would have after you finish oxford, and approx 150 + hours you could be in the right hand seat of a airliner flying with (me!) Capt's, building your experience before swapping your CPL for an ATPL.
What the adverts are implying is that you must be rated ( have gone through all the training for that type of aircraft - be it the 777 or saab 340.) The simulator (sim) is what we do every 6 months and the advert is stating you must have done your last sim within the year. Ie I know a friend who flew the saab in 1999 so even though he has experience on the saab he would not (techincally) be what they are looking for as he is now flying another airliner so therefore would not match their criteria.
Flight on type is how many hours you have flown on each aircraft. I have 1000 hours on BAe 146 type, I have 1000 DC-10 on type and now fly the A320 and have 6000 on type. So the adverts are looking for 500 hours on 777 or saab 340. Sometimes they state this but don't always find what they are looking for and so have to lower their requirements.
JAA means Joint Avaition Authority ( as in EU states/countries ) A commerical licence from the UK now might be a JAA licence; I hold a CAA (UK) licence and could exchange it for a JAA (and will do when it expires) Hope this helps