Does everybody get crushes?
The answer appears to be "yes," especially if you broaden the concept to not just on other people but also things, such as a particular car. The exact mechanism is not known, but it is related most strongly to the teenage to young adult years when the mind is rewiring itself. During this time it is very easy for people to be obsessive. When that obsession is directed at a person, it becomes "hero worship," or if it has romantic component, it is called a crush.
Crushes are characterized by thoughts about the other person popping into you head involuntarily, extreme shyness when attempting to interact with the person, and anxiety of doing something wrong to cause the other person to reject you. People with crushes don't often know the person they have a crush on -- they are too shy to talk to them. Thus, crushes are really imaginary relationships.
When a person overcomes the shyness to interact with the person, the romantic crush can develop into an infatuation for the other person. It is still mostly imaginary, but the involuntary thoughts give way to purposeful fantasizing about the other person.
Eventually reality sets in and the crush or the infatuation breaks down. It is replaced by love or the relationship ends. Generally teens and young adults have a hard time distinguishing between infatuation and love, mostly due to a lack of experience.