Huyen, "got your six" is a slang term that is mostly used in the U.S. military.

It means that someone "has your back," that they are watching out for you, making sure nothing bad happens to you.

It comes from the system that pilots use to locate objects of interest when they are flying. Imagine that the plane is in the middle of a clock face. As the pilot looks directly in front of him, that is 12 o'clock. Directly to his left is his 9 o'clock, to the right 3 o'clock. And directly behind him is 6 o'clock.

So, "got your six" would be said by another plane flying with this pilot. A plane which can see that pilot's "six."

And as we can see from your example, it is used to mean the same thing by people outside of the aviation world.

Make sense?

Wishing you success in your studies.

Robert