Follow below listed steps --
1) Copy folder vision from - integration/whmcs/modules/support/ to WHMCS installation -- /modules/support/
2) Copy config.php file from vision installation to /module/support/vision/ directory of WHMCS Installation.
example : If you have installed Vision at yourdomain.com/support/ then you should find config.php under "support" folder
3) Edit above mentioned config.php file in whmcsinstallation/module/support/vision/
Locate line -- $this->database = "";
Below this line add one more line --
$this->domain = "yourdomain.com";
Where yourdomain.com == your Vision License Domain.
4) Copy the vision directory from integration/whmcs/templates/ to templates directory of WHMCS Installation.
5) In WHMCS admin, navigate to General Configuration >> Support and choose Vision in the Support Module drop down.
That's it. You are done :)