Go to www.garena.com then click on any of the MIRROR LINKS to start downloading.
After the download is complete, run the Garena_setup.exe file
Choose the directory where you would like to install Garena.
After the installation is done, click FINISH to end the InstallShield Wizard
To run Garena, just double click on the Garena icon to start it up.
If you have any questions, feel free to post it on the comments.
It is open for anyone (no need to register)