>What's the difference between a Decker/Hacker/Technomancer/Rigger?
Decker is just another word for a hacker. It's because he doesn't use a computer but a "Deck".
Which is a super crazy expensive mega-laptop.
Technomancers don't use the deck, they magically hack with their brain/soul. (They're bad, don't be a technomancer, and don't let your friends play one)
Riggers don't really hack, they just control machines. They're not going into the matrix to steal information, or break through firewalls, they pilot drones, cars, car-drones, tanks, planes, swarms of drones.
>Likewise, what's the difference between a Shaman/Adept/Mage/Whatever else they get called in Shadowrun?
Shamans and mages used to be different kinds of spell casters way back in the day, one summoned spirits and had totems and one cast spells and dealt with elementals.
Now they're one and the same, the only difference is their outlook on how magic works.
Broadly speaking mages view magic as a bit of a science thing, with rules and as long as you follow those rules and structures you just do whatever.
Shamans have a whole "In tune with nature" thing going on.
Adepts use another kind of magic and can't cast spells (Unless they're mystic adepts), can't astral project, summon spirits, and can't perceive the astral world (Unless they take an adept power to let them do that), and instead what they do is that they channel magic through their own body to get supernatural powers.
Like an adept won't throw a fireball spell at your face, he'll turn his fists into raging infernos and then punch you. An adept won't cast a mind control spell, he'll channel magic into himself to become so convincing you *wan't* to do what he says. (Pornomancers is the fan term for a type of adept that throws a quite frankly ridiculous amount of dice in social situations)
Mystic adepts are adepts who can also cast spells and summon spirits.