Wizard
Witch, Sorcerer
noun
You know that 魔法 is "magic" so what about someone who uses magic? What are they called? How about a wizard, witch, or sorcerer?
The reading for 魔法 is what you learned with the kanji. The reading for 使い is the same as 使う.
約束を守らないと、みんなから相手にされなくなるぞ。いいから、お前が先日会ったっていう、その魔法使いを連れてこいよ！
If you don’t keep your promises people won’t take you seriously, so bring the wizard you said you met the other day!