The basic instructions are these:
1. Click this link and follow instructions there to create your Rebirth Game Account:
https://play.cityofheroesrebirth.com/public/create2. Download the Sweet Tea City of Heroes launcher installer:
https://www.cityofheroesrebirth.com/launchers/SweetTeaInstaller.exe3. After downloading, double click and run the SweetTeaInstaller.exe
4. Find and run Sweet Tea from your start menu. In the panel that appears, find the Rebirth server and icon. Select it and press the validate button. This will download and update your game files so you can start playing on Rebirth.
5. Once validation completes, with Rebirth selected click the "Play" button and get started!
But let us know if you are having any particular issues.