Just choose which country you want and click the button. Pick whichever location is closest to you, or actually closest to where the content or service you are reaching sits -- for most people that is the same thing, but it is not always, and the account works the same regardless of which one you choose.
Trojan does not try to hide that it is encrypted -- it tries to look exactly like a normal HTTPS website. The server speaks real TLS on 443 and, to anyone connecting without the right password, serves an ordinary web page and nothing else.
