Concern is both a noun and a verb. As a noun it's something that you find particularly important. If you love pizza, getting the crust just so is a major concern during your pizza party.
Concern can also be something or someone that makes you upset or anxious, like your concern over the quality of the pizza crust. It can be a feeling of sympathy, like when your mom expresses concern over your obsession with pizza crust. As a verb, concern means to be relevant to something. Your main goal today may concern studying for your math test. Concern can also describe worry. When you stay out past curfew, your mom will be concerned.