Becoming a Broker vs Principle Broker?

[Isaac Conrow]

I'm looking to get my real estate license but the only options I can see for a license are either broker or principle broker. I'm located in Oregon and I'm going through Oregon.gov for a potential real estate course. I have a couple questions. 

The only way to become an agent is to get one of these licenses? 

What is the big difference between being a broker and a principle broker? 

Am I still able to work for an agency if I become a broker?

Lastly, would anybody have a recommendation on where I should go to get licensed (online)?