I can't tell whether or not I am attracted to anyone, romantically or sexually. How do I find this out?

You can try to analyze your feelings and sensations about boys and girls, maybe try to imagine yourself with different people in sexual and romantic contexts and be honest with yourself about how that makes you feel. Your emotional and physical responses to these fantasies will give you a hint of your orientation. Also, remember that some people have a lower sexual or romantic drive than others, but it doesn't necessarily mean they're asexual/aromantic.

This depends on how old you are. Until you are through puberty, you cannot know any of these things for sure. If you are past puberty completely, then if you have not been specifically attracted to anyone, then you may be aro ace. If you have been, then you are not. If you are not past puberty, then all you can do is wait. You may think you know, but you can’t make definitive statements. I don’t really know how to make this fully fit the word count, so the rest of this answer is to fill that in completely.