In order to connect to your Volusion account, FarApp requires a username, encrypted password, and endpoint. The username should belong to an administrator account in Volusion. To obtain the encrypted password for that account, please see this link: Volusion API. Specifically, you will want to consult the Accessing API Help section to find the Integration Help page, and then the Obtaining Connection Information section for instructions on finding the password. Lastly, the endpoint should be the URL of your store.
You should also make sure that the account with which you provide FarApp has the necessary permissions; instructions for editing account permissions can be found here: Volusion Admin Access