Well.... The sales post did explain how to operate them (And I agree with the other poster that it is likely a park model, more on that in a bit)
It says "1981 Oak Park Trailer. 35ft. 2 pullout sections. "
So to operate them you remove any lock bars or pins that might exist and you PULL (or push)
Actually.. here is what you do While it's up on it's wheels crawl around under it and look at the underside of the pull out sections.. If there is a track and motor,,, Then you need to put 12vdc (most likely) to the motor, this can be done using a temporary battery if the rig does not have a good battery in it. Applied one way the motors will move the slides out, the other way in, However I'd not be surprised to find there is no motor.
Park models usually have no on board water storage of any kind, they are designed to be hooked up to water, sewer and power so they do not have a potable water tank like my Motor Home does, they often do not have black or gray tanks (Though they might) and they may well not have a "house" battery, even appliances may or may not be "dual power" (lp/110) or 110 only, and LP may or may not be onboard storage though I think most have an LP frige and furnance with onboard storage or at least optional on board storage