Re: tapered leader became a knotted leader...
Those are called "wind knots" usually caused by poor timing. A common beginner fault is not stopping or pausing long enough to let the line completely straighten out between the back cast and forward cast in effect whipping the fly line. "Whippers" also have a tendency to cast on an arc rather than a straight plane. You did well to notice your casting plane problem so soon.
Force yourself to throw a high back cast up and over your shoulder and watch your back cast. Accelerate through the back cast coming to a sudden stop (speed up and stop). Watch the line straighten out behind you and then come forward with the cast. The timing of this little pause between the back and forward cast is critical to making a good forward cast. It is really a matter of practise to get the timing and mechanics down ("muscle memory").
I cannot emphasize enough the importance of a high back cast when learning the basics. It is so much easier to watch and control the cast keeping it on a straight plane if you start with a high back cast. At the same time, it is just impossible to break your wrist (drop your thumb back) and throw a high back cast . If you throw a low back cast (lower than your shoulder which is often the result of a "broken" wrist), you have thrown an arcing backcast and usually end up arcing the forward cast as well to prevent hitting yourself with the fly.
Tight lines and keep your back cast up!!