How do you know if you have a crush on someone?
Music. If a song comes on that talks about relationships (pretty much every song) and his/her name pops in ur head, it's a big sign that u have feelings for them.
You just do. It comes naturally. If you find yourself staring or looking in the way of that person a lot, it is likely.
If you ever think about him/her and if you dream or daydream about them