[Melusine]

To answer number two, scribing magic into your spellbook is done by talking to people who have "Spells" as an option (Where it says "Barter", "Training", "Enchanting", etc.). You buy the spell you want from them and then it will be added to your repetoire. I'm guessing you are in Balmora: there are several people in the Mage Guild building who can teach you spells, and possibly in the Temple as well.

As for guild quests, you might want to go outside, into the open fields, and practise your fighting skills for a bit first. Slay lots of rats, nix-hounds, mudcrabs, etc. Then when your major and minor skills have improved sufficiently and maybe you even gained some levels, it will get easier.
I have Light Armour as a minor skill myself and I've used Chitin Armour from the beginning without running into too much trouble. Whichever armour you wear will become increasingly more effective the longer you wear it. There's an armorer in Balmora across the road from the Mage Guild. Be sure to remember having an armorer repair your armor and weapons every once in a while: they deteriorate and become less effective with use. You can also train your armorer skill and do it yourself.