Your knowledge on technology is restricted, focusing on the entirety of the tech base of the United Nations Space Command. With this knowledge, you can make the Spartan programs, construct ships like the UNSC Infinity, and create the MJOLNIR armor.
Optionally, you can become an augmented super soldier, a Spartan II. The genetic peak of humanity was enhanced even further, gifted with enhanced durability, reflexes, and the MJOLNIR Mk VI powered armor.