When you Astrally Project or go into Full VR (As opposed to farting around in Astral Perception or Augmented Reality Vision), your body ragdolls and drops. With some practice, you can do it sitting up, usually leaning drunkenly against a buddy. (An early novel has a character trying this for the first time and face-planting into his soup in the deli, IIRC.).
With Riggers, they become the machine they're in. They see with the cameras, feel with the touch sensors on the metal, smell the radar, and so on. It's like being the Machine. They just get a new body.
With Deckers/Hackers, you're in The Matrix, which has NOTHING to do with that movie. Think more Snow Crash (If you've read it), or Johnny Mnemonic when Johnny is making "A phone call". What you see is a virtual world of (mostly) photo-realistic objects that do not obey the laws of physics. An Adobe Fortress (Like the Alamo) floating in the air with cannons all around would be the Lone Star Site, for example. Or a Stepped Pyramid for Aztechnology. Don't forget lots of glowing things and "Neon-like effects" on everything, even if they don't fit. MC Escher could have designed real buildings in the Matrix. Every place has a different style or setting. Seattle, for instance, known as the Emerald City, has a lot of green effects, and their government buildings are right out of The Wizard Of Oz, with "Guest" users using public terminals (Payphones, and about as easy to find as they are today!) being generic non-sexual green "Golems".
With Magicians, you're actually stepping beside the frame of reality, and entering a world that has more in mind with emotions and souls than with physical natures. You see people's auras (And, with training, can learn to recognize them like you would a person's face.). You don't see words on signs for example, but you see the emotional impact that people have affiliated with the signs (A street sign would show up as nothing as no one invests any emotion into it, but a sign for a strip club would show a bit of lust.). This is a very alien place and very different than any kind of human perception (The VR stuff of Riggers and Deckers/Hackers were built with Humans in mind, the Astral Plane wasn't.), and has to be experienced and cannot be explained easily. That's not a cop-out, it's how it is. Keeps magicians mysterious and keeps them able to ask for a higher wage than the rest of the team. (That, and being able to think people dead. Always a handy skill.).
So, to sum up: AR/Astral Perception you're walking around like any other John Q. Wageslave on the street. VR/Astral Projection, you're sprawled out on the floor, your body helpless while your brain is busy elsewhere. A common statement about doing something while in this state is, "Watch my shoes" or "Watch the meat", meaning the body.
Now, as for the character creation... I'd suggest reading through the character creation examples with people before starting, and making sure that people have a good idea of what they want to start with before they begin. It's an open and points-based system, you can create anything you want, so there's lots of options and getting distracted can easily be done, and you don't have to "See how I rolled" to figure out your character.
