I have a breaker on my panel that has 2 white wires and one black and a test button. I am changing to a breaker that has no white wires going to it just the black. Do I put both white wires to the bar or only the bigger one?
First, it sounds like the old breaker is a GFCI or AFCI, and the new one is not. Changing types like that is likely a code violation and can compromise the safety of your electrical system. Do not do this unless you know why a GFCI or AFCI breaker was installed and that you have removed the conditions from that branch circuit that required their installation.
Second, since you are asking this type of question, you likely don't have the experience to do this safely. At this point, I recommend you hire an electrician.
If you insist on continuing and have confirmed that it is safe to remove the GFCI or AFCI breaker, then start by tracing the white wires. One should be going to a bus bar in the breaker box and the other should be exiting the box with the black wire. Disconnect the one wire from the bus bar, and connect the other one to the bus bar in its place.
It's possible that code might require this to be an AFCI/GFCI breaker, so you might be violating code if you do this, fair warning.
With that said, the black wire is the hot wire, which should go to the new breaker. The white wire is the neutral, which should go to your neutral bus.
Your question itself shows that you only have a passing familiarity with electrical work, which is a red flag. If you want to do this yourself, be aware that you likely need to learn more about the basics of electricity before opening, and working with your electrical panel.
With that said, this isn't rocket surgery. As long as you understand what you're doing, you don't have to be afraid of everything instantly killing yourself, or setting your house on fire. Those are real, valid concerns that people have, but they can be easily addressed by the average person with a little education about basic practices.