State tax filing

Thank you for the help I am trying to teach myself the ins and outs of running a "sole prop."  I am currently a full time grad-student and currently living off savings for this year. My only income will indeed be relatively small from my KDP Ebook sales this year (unless something crazy happens). I have been attempting to decipher the tax brackets for the state. To me its extremely confusing. I thought I understood the tax bracket for self employment to be at 15% of what your income is above the $400 plus a payment of say 10% to the IRS for any royalties under $9,500. Apparently not.  Again, I appreciate the help!