Corporate or LLC...Whats The Difference? Who Am I?

I'm starting my own business. I know what DBA means, and I'm the sole owner and trying to apply for all the proper licenses (and name availability). The question keeps coming up, am I a Corporation? I say "No" but what is the correct category for me? Also, do I have to pay for my business name to be registered? I'm going for online retail...I know I need a "Retail Certificate" and "Local Resale License". Do I need anything else???? Your input is really appreciated. Thanks!