Piracy is a necessity for Story Mode. As said in the Start page, it's better to pirate it than anything. You have two options:
Download from GOG-Games (For newbies)
**Season One Download Season Two Download**
Torrent from Fitgirl Repacks (Use a VPN, for experienced users)
**Season One Torrent Season Two Torrent**
Use an adblocker. If you’re torrenting, use a VPN (Virtual Private Network). DO NOT USE A FREE VPN. Also ensure if you're torrenting to click the the links that say "magnet", they open your torrent client directly. It's more convenient than having to navigate file hosting sites. The only good torrent client we'd recommend **qBittorrent.** If you would like a guide on torrenting, it can be found here.)
"just pirate it bro" - DroidTheAwesome
You can buy the physical PC disc off of Amazon, eBay or another trusted site, Season Two’s PC physical copy does not contain episodes 2-5 and there is no way to download the episodes without pirating them (ie: It’s a waste of money.)
Steam keys are a mixed bag. You may get your account suspended and can easily get scammed. You aren't supporting Mojang or Telltale. It isn’t worth the risk and the only people you’ll be supporting are the scalpers who sell the game for exorbitant prices, but if you’re insistent on it, get a key from G2A.