How do you know when you're attracted to someone?

You can say that you have a crush on a person if you have a feeling for Him/Her and you care what is happening in His/Her life and you love whatever His/Her personality type is. You can say that you have a crush of improving feelings for Him/Her if you find personalities of a person you like that person has. You try to find out some stuff about that person to see if you're compatible. I would say that you know when you have a crush on someone when you start thinking about them every minute of the day, you care about them in a way that you wouldn't usually and you always care about what they think about you. You get a weird feeling in your stomach when they are around you.