SID (Standard Instrument Departure) and STAR (Standard Terminal ARrivals) are, as you would guess, standardized routes into and out of congested airspace, put there to take some of the workload off of the controllers.
As for how to fly them, there are several ways of doing it in FS
1) The Agonizing but Cheap Way: You'll need to find the chart for the appropriate SID or STAR. VATSIM sites will have a lot of them (www.vatsim.net, and then search the appropriate region, country, etc.). Once you've done that, you can load each of the waypoints into the FS
flight planner and have the GPS follow it. There are several reasons why I don't recommend you do this. Firstly, it's a real pain in the ass and takes a long time. Secondly, in all probability there will be a point or two along the SID or STAR that don't exist in the FS
planner for whatever reason, and thus you're kind of stuck. Thirdly, some SIDs require vectors to a certain point. You can't exactly plan for vectors, and when you get cleared direct to your first fix, putting that into the GPS will throw out your entire route (did I mention the FS
flight planner and GPS suck?)
2) The Perhaps Difficult to Learn But Highly Rewarding Way: For this way, you'll also need a chart for the SID or STAR. Once you've got that, you can follow it to the end, and then engage your GPS route. You'll need to know how to track VORs, NDBs, and intercept VOR radials, etc, which is what makes this difficult for some people. Tracking direct to a VOR is one thing - flying a heading to intercept a radial is another. However, you will come away from it a much better pilot, and you'll never have trouble with instrument flight again.
3) The Easy but Costly Way: Get FSNavigator from www.fsnavigator.com.
It allows you to create a flightplan with SIDs or STARs and import it to your flight planner and fly them with the GPS. A few downsides to this: 1) FS
Navigator is a fantastic program, but it is payware. 2) You'll still have the problem with vectors that I mentioned earlier. 3) Not all SIDs are included in FSNavigator (mostly the ones that are almost entirely vectors - JFK
4) The Whimpy Way: Inform ATC that you are unable to fly a SID or STAR. You'll have to tell them about the STAR, but you can file your flight plan with "NO DP
" in the comments section, indicating that you are unable to fly a SID. You'll probably irritate the ATC and perhaps wind up in a holding pattern somewhere, but you won't have to worry about anything. If the ATC is nice, they may offer to vector you along the SID or STAR, and you should by all means accept the offer, but you should never ask for them to do that - it makes you look like you're extremely lazy, and they're likely to take out their frustrations on your fuel load.
Personally, I recommend option #2. You can use the autopilot for it - you'll just have to be more involved during the departure and arrival phases. But heck, that's what realism is all about, isn't it?