Validators are set up in the Validator Setup Activity and are used to validate manual and EDI Bills as well as Tenant Bills.
There is a more information regarding Validators in the general help - click here.
On the Welcome page, click on Validator Setup
To set up one or all of the Tenant Billing Validators, click on 
Change the Type to Tenant bill
Click on the Definition dropdown to see the four available Validators
Click here to see how to set up a Validator.