wtf do i have to download?

i am sent here from an email thats late according to the email sent before about preloading. What a confusing mess this is to play. am i looking for a launcher? xbox app? insider app?

i hate the spartan boots on ground -Yoink- in air how do you not know what the waypoint is, did you fall off after reach? talk im getting from 343

wont look at comments, just feedback on how it feels from someone who hasnt played halo since reach

Use the code they gave you on Steam.