Tree of Savior Korean Server (OBT) will be out tomorrow (17/12/2015). NA/EU/International server will be out on Q2 2016. In this guide you learn how to get account, download game and Korean server rules.
Tree of Savior Korean Server Guide

How to get Tree of Savior Korea server account
Because Koreans laws you can't register account without confirming your ID and we can't fake it.
1. Ask your friends who live in Korea to make you account.
2. Buy him.
Enter https://www.obtgame.com/?ac=1451 and than chose - Verified Tree of Savior Nexon Korean OBT Account. After payment done they send login and password in 24h. It safe and most people use this service.

Now enter nexon website http://tos.nexon.com/main/index.aspx put login and password and press button that located on right. After this you can be redirected to other nexon page where you see your login, password and captcha.  Fill them again and press confirm button.

Download ToS KR client
http://tos.nexon.com/customer/download.aspx
Press on big orange (color can be different) button, accept everything it want and press left button.
Some browsers/adblockers can block downloading.

After you download installer, open it and press on left purple button.

To launch Tree of Savior you must login on http://tos.nexon.com/main/index.aspx and press big blue button. If everything successful you will see game patcher.

Nexon Korea Server Rules
I don't know if they need here but better know them.
First and only rule - Never speak on English Language (and others languages except Korean) in chat. You can be reported and banned. You can't restore your account if you get banned.

English patch 
Download and read - how to use.
https://mega.nz/#!KBl3lCoI!hN3IzEuKCGp26Zg1kxCRWz9csmOuBItXRyEe4UuONL8