Prt scr button. Screenshots are stored in your C:\Program Files\Auran\TRS200X\Screenshots folder. Just be warned that the screenshots that you take in Trainz are in .tga format. You'll need a program like IrfanView.
You go to your C:\Program Files\Auran\TRS200X\Screenshots folder and open up the pictures with IrfanView and save them as .jpg and then you can upload it to your favorite image hosting site for all to view.