how do i add a special effect?

so if you cast a spell, a special effect starts under you and grows in size? so like for example, that graphic for flamestrike and then it gets bigger to a bigger area surrounding you?

um...i dont understand the question at all..special effects are all different models with animations, some will grow in size, others decrease in size, some just sit there and...yeah

Most of the effect models cannot be resized at all within the editor because they are made out of emitters, not poly.
The flame strike is in fact made out of a very small flaming part spawned several times within the spell's area of effect. You can do something similar using triggers, that shouldn't be too hard.