Kevin it is hard to teach someone to cast a bait caster with out being there in person. With that said I will attempt to help:
First there are adjustments on the reel which will help the reel from over running which cause your backlash, they will be on the side of the reel one side or the other some reels have a dial with numbers others have a small knob. You need to mess with these until when you release your reel holding the rod parallel to the ground your bait falls slowly to the ground.
Second do not try casting real hard. Jimmy Rodgers who was one of the finest trick caters who was sponsored by Lews reel said he could teach anyone to cast for five to ten bucks. He would have them put a five dollar bill between there elbow and their side with the rod parallel to the ground then turn the rod until the reel handles faced up, next with there wrist they were to bring the rod tip up over their shoulder and then bring it back down with their wrist. If the five dollar bill fell to the ground he gets to keep it. The trick here is do not over cast; make it very smooth and easy and keep your thumb on the spool and stop the reel turning just before the lure hits the water. As you get better and better you can increase the speed of the rod and lengthen the distance. The lure has to travel faster than the spool and pull the line off the reel if the spool is faster than the lure is traveling you will have backlash.