Pulling a trailer with disc brakes.

My truck (2008 Sierra)has a trailer connector that is round, I have an adaptor that plugs in and gives me the 4 flat that I am used to using.

If the trailer has brakes what do I need to use them?

Can I pull the trailer with my current plug and not use the brakes on the trailer?

Can I pull the trailer at all without using the brakes?

I am clueless on this, please help!