You have to install the integrator 3 software and the wordpress plugins for it to work.
To install the integrator 3 software create a folder on your server e.g. integrator
Then run the install
After completed login to the admin area to setup your wordpress and whmcs connections.
The API info has to be generated in whmcs and the info entered into the wordpress plugins so that it will call the whmcs system using the api to get client info and ect..