Your original question has been asked many times before. This forum has a great
Search tool which
you should use. Try entering something like "difference between abstract class and interface". I'm sure you will get a lot of discussions on this topic that will answer your question. If you still need help understanding let us know.
As for your second question, I'm not sure what you mean. Can you give some context? Where did you hear or read the phrase "it is loaded dynamically"? Perhaps more importantly, what does "it" refer to?
Layne