They will appear under Quick Drive. There are two tutorials as Standard scenario (the one in the video is the English tutorial.)
I can only guess why it's not available through steam. The biggest legal problem probably has to do with liveries. Also is Chris willing to constant update and improve his models which is much more rigid once he brings his models to steam. And lastly, Chris is much more interested in Dutch train models which is problematic given that there are no Dutch routes available through steam either.

The3oLand, Thank you!!! So after installation it will just appear in TS 2016? I ve used to buy only steam addons, so I'm a bit frustrated how to get his one, why it is not in steam? :(( It is so perfect.

See http://www.christrains.com/ts_product_stadlerGTW.html
About 11 paint schemes/color variants most of the Dutch. There are also the following non-Dutch variants: German ODEG, Swiss SBB Thurbo and USA Capital Metro (Texas).
Installation is done by an executable.

Did someone already buy this addon? How do you install it? What does it contain? Does it have all color variants of stadler? How many color skins in the addon?

Please guide me how to buy and install this addon, I love this train and watching it every weekend with my young kid, so he would be very surprised to find this train in his TS2016 simulator :)

what train sim is this then ts16 ? it's awesome! too I also can't wait when they bring underground in TS16 too thats goign to so awesome! :)

Either directly from ChrisTrains at www.christrains.com or alternatively at the various addon resellers such as JustTrains, Aerosoft etc. I recommend to buy directly from Chris as you get automatic life time support.

How can I buy it?

The GTW diesel and electric variants are available at http://www.christrains.com/ts_product_stadlerGTW.html . Chris is also working on a Swiss Turbo variant which will be available later as a free upgrade.

nice! view :)