Never played halo. What is it about?
In the original HALO, they drop you in a suit of armor with a jump jet, and a limited supply of fuel and ammunition; and you had to perform various missions.
When you learn to navigate and kill things before they kill you, then you have to go find fuel & stuff and learn how to detect it. You have to go rescue somebody in trouble....various missions.
Then they give you a small squad, and some things to capture or destroy, thus the missions continue.
I only played the early review version of the original HALO, and I did not buy the official release version with all the levels. It might be because it required a voodoo card and my wife had the voodoo machine while I had the open GL machine. I generally did not buy games that required a voodoo card but I did upgrade one of our computers to a Voodoo 3