I can try my best and I'll try and make it fairly simple for you. You can use the FMC fairly briefly or you can use it to its fullest extent like it is used in the real world, I would advise you to use it briefly first until you get to grips with it. Once you get to grips with the FMC it will be your way of managing the aircraft during flight.
Firstly you will come to the INIT REF page, this basically allows you to access the initialisation and reference pages and also the performance where you can enter all your loading figures (ZFW etc) and your cruising altitude for your flight. Then you will come to the RTE (Route) page where you will enter your departure and arrival airports using the 4 digit identifiers (i.e. EGLL for Heathrow). The RTE page is also where you will enter your flight plan, inputting the airways on the left (i.e. UL612) and waypoints (i.e. RESMI) on the right. Then you will come to the CLB (Climb), CRZ (Cruise), and DES (Descent) pages detailing the performance of the aircraft in those sectors of flight. The DIR INTC page is next and this is where you can go direct to any waypoint on the flight plan. Next is the LEGS page, very important and one of the most used pages - this shows your route that you have imputed into the RTE page with all the speeds and altitudes. The DEPARR is a page where you will select your departure and arrival routes into the airports where you are flying from/to, also the runways for the departure/approach. The HOLD page is next, and is fairly self explanatory; here you can hold over any navigation point on your flight plan. The PROG page shows your flight progress information and also the times expected to arrive at your destination airport, the estimated fuel figures are displayed here also for the various points in your flight. The next one is the EXEC light, this is just a button to execute any changes made in the FMC, and it will flash up when required. The next button brings you to the N1 LIMIT page, here you can select the thrust requirements for your flight, but this is fairly complicated so I suggest you leave the settings as they are.
That above is my best attempt at a very brief depiction of the FMC and I hope it suffices for the time being, if you need to know in any more depth please ask.
LAST FLIGHTS= Ryanair LPL-BGY-LPL - EI-DPS/DWV - MAY 08 // NEXT FLIGHTS= TBC