I remember when I was able to train magic with a shield that contributed to my defense exp. Can I still do that or do I have to train defense with ranged or melee and if yes, how. Thank you.

In your mage book there shold be a little shield in the lower left corner for defensive casting.

^What he said.

 

You shouldn't defensive cast unless you're a mage pure though since defensive casting reduces your magic exp which is both slower to get and more expensive to get. I'd recommend getting the defence levels with melee for maximum speed and minimum cost.