I want to be able to play this on my steam account how do i go about obtaining the key that i just bought for this game i know how to download it and etc. I just want to be able to play it on my steam officially and not through the add non steam games

When buying it here (GOG), you are buying it DRM-free, meaning there won't be anything you need to use in order to play it - you simply just download it and play.
Buying something from here, won't give you the game for Steam. If someone told you that, then you were mislead.