FWIW, I actually started down the path of becoming a VatSim controller. I can definitely see why a lot of people are intimidated to connect and talk. Frankly some nights the traffic on VatSim is close to RL, especially CHI, ATL and LAX, and East Coast in the USA.
If it helps, I found that just getting the voice client installed and connected and doing some short VFR flights around lower volume airports is the way to go.
VatSim uses a ‘top down’ approach to controlling so, anywhere the is a center controller, you can get all the services (clearance delivery, Ground, APP/Departure and Center). If you are not ready for, say tower, find a place with only Ground and that way, once your handed off to tower, its ‘unicom’. Also, there is no rule that says you can’t just hop on and file a flight plan and log off. Obviously, it would be a pain if every one did it all the time but, if you start in small chunks, your ‘phraseology’ will improve to the point where, for example, asking for VFR or even IFR clearance is easy, second nature.
Remember, most of the volunteers on VatSim are hobbyist themselves, their chosen hobby being, ATC. They are no always perfect and most won’t expect you to be either. If you run across a controller that is rude, just close the client and keep flying, try again with a different controller. I have found, using VatSim for a couple months now, only 1 o of the many many controllers to be a tad rude. That was CHI and I can understand. A lot of new VatSim users want to jump on and get in the CHI or ATL airports and that does cause problems.
Do yourself a favor, start somewhere like KS or MEM (KMEM). I know personally the KMEM team is very kind, things are typically less chaotic at MEM than say, LAX. It is up to you to google the FAA/AIM rules (google IFR or VFR phraseology) and learn the processes. It can be a lot but, if you really want to interact with a live ATC virtual or not, you need to be responsible and prepare yourself. If you make a mistake, many times, it is no big deal. About the only mistakes that will get you a ‘good talking to’ are things like, taxing across runways without clearance, well, taxing without clearance at all is a no-no, taking off without clearance, landing with out clearance or wrong runway, which happens on occasion. Most of that is mechanical stuff though, what a new virtual ATC user needs to start with, strictly my opinion, is just learning to call in on the right frequency with ATIS information in hand, and filing a simple VFR then eventually IFR plans (All by the way, covered on the FAA site).
The more prepared you are by reading the FAA and related documents the better. Also, I highly recommend, just logging in and listening to the various controllers. You can literally start practicing what to say and know what to expect just by listening in. You can be sitting on the ground in your vCockpit just listening, no harm there at all.
Also, lots of videos out there of people using the VatSim network, real life examples of the various kinds of requests and responses.
I will say having started down the ATC path, they pretty thorough. They take their controllers very seriously and do not let just anyone join and jump on and start ATC work. There is a fair amount of time these volunteers, some real life ATC people, put into their chosen hobby. Many are also sim pilots just like you so, they know what its like to be new and also understand when your just off the runway and the ■■■■ 747-800 FMC starts circling : ) There is no shame in saying, ‘hey, sim issue, Im gonna log off, etc’. The VatSim network isn’t perfect and neither is the sim software nor the pilots.
Again, just re-stating, you can always log on and observe, and by all means, don’t be ‘that guy’ they have to basically train while trying to service other pilots. Make some effort to learn the basic processes, like how to file a flight plan, then, don’t be afraid to key up the mic and start. The sooner you do, the sooner you’ll have a few hours of online ATC time, the sooner it will become 2nd nature.
Oh, almost forgot, someone mentioned, you cannot in fact, be on the VatSim network and ignore controllers once your in flight. You will get contacted by a VatSim ‘manager’ who will remind you that you are expected to respond to controllers as part of their EULA/Terms/policy/etc. If your making long flights and need to step away, you can request it but, be prepared to be asked to sign off if you are not going to participate. There ways to kind of get around this but, if your new to the system, best follow the law : )
Lastly, for real this time, 1, do not be afraid to keep a paper and a working pen near you. Real pilots do it or have co-pilots, so dont hesitate to write down the information, like IFR clearances, if you need to, no shame in that. Don’t be afraid you talking back too slowly if you need to read it back off of paper, its all good. Also, if the the controller is talking too fast, or low or you cannot understand, don’t be afraid to ask them to repeat for you. Most times, I find, they get the hint. Not everyone does this every day for a living, so, they will slow down if you ask them to repeat or just ask them to slow down a little. A couple weeks, and you will be the one speaking too fast lol.
PLEASE, have the phonetic alphabet tapped on your desk or handy. This is probably the number 1 most confusing communication piece. If you know it great, if not, have it on hand and start learning it. Also, PLEASE use SkyVector or similar to start looking at charts. If you are going to fly IFR, you need to start learning how to read STARS, SIDs and landing procedures. If it sounds like a lot, it is. For some, FS is a game, thats fine. For others, it is an immersive sim experience, giving yourself ground school (Again, the explanation of all this is on the FAA site!), is going to be needed. Simple VFR with ATC has processes, start there, then work up to IFR then maybe on to the airliners and jets etc. Again, just my opinion.
Anyway, its there to help us have fun so, use it but, do your part to prepare!
Have fun!
I get where you’re going, but let’s try to stick by the book; it will only negatively affect the new user.. 
But, and a big but (no pun intended)
