I was reading on fission bombs the other day and it sounds very simple on how to make a nuclear bomb. I just want to know if I'm understanding this or not.

1. Get a sphere of U-235 and mold U-238 around the sphere to create a tamper.
2. Shoot a U-235 bullet at the tamper.
3. Detonates.

That sounds too simple to be true!

Very basically yes.
This is one of the designs they used during WW2, but it produces a very large bomb, in terms of size and mass, for a relatively small detonation.

The modern method is shaped explosives and enrichment with Plutonium.

These are known as Gun and Implosion types.
http://en.wikipedia.org/wiki/Nuclear_weapons - good place to start.