+1 on previous comments. You need both seat and shorts. Even then you may need to do a bunch of riding to toughen the butt if you are going to spend some hours in the saddle.

Everyone has their favorite brand and kind of chamois shorts. A lot depends on the individual rider and how long you ride. For short rides around town I don't use any padding. For longer rides I wear a good pair of padded shorts. When out on the hybrid for a morning just nosing around I'll wear a thinner fabric but very well padded pair of shorts under my street clothes. But that is just me. You'll figure out your own thing.