No one is powerful spell caster. "With knowledge comes power" or something like that. Study the basics of magic, and over time you'll will be able to cast spells. Remember spells don't work all the time or they will backfire on you. Also, spells don't work right away, give it a few weeks. The best teacher is yourself.
As stated from above, there is no such thing as a "powerful" spell caster, it's like stating there are levels in magick, which there are not. Understand that knowledge is the power. No one will spoon feed their knowledge to you. Some people will although send you to resources that will help.