Sure. ((OoC: You'll have to bear with me throughout this; the magic in Fairy Tail isn't well-defined in comparison to some other series.)) Magic can be broken down into two basic types, it seems: internal and external. Internal is magic that is generated by your own body, such as breathing fire or shape-shifting, while external is magic that involves objects, like summoning creatures from other dimensions or my type of magic, ex-quip, which lets me summon weapons or armour.

If you're good with a certain type, it will be easier for you to learn magic of that type over magic of the other type. For example, of my friends, Natsu can breathe fire, so it was easier for him to learn how to shape-shift, while Lucy summons spirits to fight alongside her, so shape-shifting was much more difficult for her to learn. Do you follow?