i bought twau on amazon but will it activate on steam so i can get achievements?
Looking at the description on amazon.com it says "Telltale account required for game activation and installation" so I'm gonna say no, it won't activate on Steam.
My experience is that if you want Steam version then it's easiest to buy the game directly from Steam and if you want TTG version then it's easiest to buy it directly from TTG. Buying from a third party always requires careful research before the purchase, so you can be sure that you'll get what you want and there will be no disappointments.
The version sold by Amazon can only be activated on the Telltale Store.
Telltale's own HalfbakedScheme
Confirming what corruptbiggins said, no Steam activation is possible here.
You bought from Amazon, so it essentially is a Telltale Store purchase.