Word of advice, read the entire book cover to cover 3 times. Don't worry if it takes you a month or two 
The reason why I say this is because SR is very complex and has a lot hidden in the rules that make some character ideas unattainable.
Generally the split is called the Magic-Tech Divide. Basically Magic and technology do not play well together... the more tech you have in your body, the less powerful and more dangerous to use magic becomes! To the point that if you have too much tech in you (cyberware, bioware) you just CAN NOT use magic.... or ysing magic does more damage to you then your target!
To be fair, if your character's starting Essence is so low that you have 0 Magic, Maximum 0 coming out of the gate, not being able to use flashy spells is not your (or your character's) biggest problem.
What follows is why Magic is Not Your Friend.
Let's look at the Healing Modifier Chart, at the bottom of it (buried on page 208, by the way). "Patient has implants": -1 per 2 full points of lost Essence.
Now look one up from there. "Patient is Awakened or Emerged" (i.e., does magicky things with mana or code): -2
A few lines further up, because it's always raining on a poor chummer's head, is some more bad news. "Bad conditions (combat, bad weather, swamp)": -3
After your character gets shot up one side and down the other (Because "Geek the mage first!"), they've got -7 dice to any Healing check. As Senko's explained, Resources is probably not a high enough Priority to have a very good medkit on hand. That means that someone other than you needs to be a very good doctor and very close by, or your character is going to be burning Edge to survive long enough to spend the next run in the hospital ("Shadowrun Concepts", p. 57)
This assumes you haven't taken the Negative Qualities "Low Pain Tolerance" (p. 82) and/or "Slow Healer" (p. 122 of Run Faster, for Changelings)
There ARE health spells in the game. Spellcasting 6 + Magic 1 + -7 in modifiers = at least you get to roll the default 1d6. That's a 33% chance to heal 1 point of physical damage. Roll Logic or Charisma, plus Willpower dice to reduce the incoming 2 points of stun damage from Drain.
Let's say you want to cast Combat Sense, to find your enemies before they can fill you up with bullets. That's fair, right? Spellcasting 6 + Magic 1 = 7d6 dice pool for a Force 1 spell, with a limit of 1, default drain value of 2, for +1 to Reaction when Surprised, etc. There's a decent chance of taking 0 or 1 Stun from Drain instead of 2.
Someone then tells you that you could "over-cast" for a Force 2 spell, and roll 8 dice to ... you could just buy 2 hits from that pool (p. 45 "Buying Hits"). +2 beats +1, right? You could even use reagents (p. 316) to increase your Limit, and have a chance to roll more than 2 hits. At this point, your GM should be at least smirking. Page 281, under "Step 4, Cast Spell" is "if the number of hits (not net hits) you get (after applying the Limit or Edge spanding) exceeds your Magic rating, the spell's Drain is Physical instead of Stun damage". Why is your GM chuckling?
If the Powers What Be really don't like you, you've just rolled 6-8 hits of Physical damage and now need to look up "Wound Modifiers" (p. 169-170), "Knockdown" (p. 194), "Melee Modifiers" (+1 if opponent is prone, p.187), "Defense Modifiers" (-2 for you being prone, p. 189). Now, go back up a few paragraphs, to check all the minuses to healing that 6-8 points of brand-new, still smoking, points of pain.
As some street brat nicks your credsticks, File the results under "Worst. 120 Nuyen Spent. Ever." (6 drams of reagents, p.461, "Magical Supplies").
After all this, your character, sadder and wiser, probably wished they'd stuck to learning Arcana as a hobby, and studying Parabotany, Parazoology (You never know when you'll need them, until it's too late!) as college electives.
Or, maybe becoming an Aspected Magician - can go as low as Priority D at character generation, but can still astrally perceive and maybe do some enchantment for the team in down-time - may work a bit better.
‘The difficult we do immediately, the impossible takes a little longer.’
Word of advice, read the entire book cover to cover 3 times. Don't worry if it takes you a month or two
So true, I'm quoting it twice!
Now a bit of disclosure: I'm on my first Shadowrun character and campaign (SR4A) myself. Magic can be fun, once you get the hang of it! The right spell or summoning at the right time will remind everyone around you that the First Rule of Combat is "Geek the Mage".
The poor sod's a bit of a non-optimized generalist - the sort of character people are recommending you don't build. This is because:
a) His dice pools are rarely great, and never maxed out. Not that it matters much, the way I roll.
b) It's tripled the number of rules I need to keep track of. Thumbing through multiple books does slow down play.
On the other hand, he can back up nearly each member of the team in their primary tasks. In an ongoing campaign, that teamwork edge has been well worth the trouble of looking up another set of tables/rules.
