Perhaps you've read about the cake analogy: sex is like chocolate cake. Some people like it; some people don't. Suppose you've never had chocolate cake. If you've never wanted to try it and even after knowing about it, you still have absolutely no desire to try it, it's perfectly fine to say you're not interested.
In asexdom, you'll find various analogies to explain things. Some have more fans than others. Recently, I was trying to think of new analogies for asexuality, and here's one I came up with.
Puppies. Asexuality is like puppies. They're so cute and lovable and fun to play with, and you just wanna give 'em a great big hug. But no matter how much you like them, when they mount your leg, it's just like, "I don't think I'm comfortable with this." Asexuality is like that, except instead of puppies, people, and instead of your leg...
On second thought, perhaps I need to take my parable back to the verisimilitudinal drawing board.