On your unit there are TWO  RF COAXIAL connectors

RF OUT > is the output you inject to your TV Coaxial Distribution ( connects to your wall tv socket / to your tv distribution box / to your coaxial splitter )

RF IN > is an ATTENUATED port typically used to connect a local TV for monitoring  

PLEASE NOTE: the built-in PASSIVE SPLITTER can also pass signals from the OUT to the IN port ( reverse channels forwarding ) and it applies an attenuation of approx 10 decibels

To combine multiple VeCOAX UNITS and keep the signal between units perfect and balanced, we suggest to use any generic multi way coaxial splitter which are normally bi-directional and can be used as combiners and/or splitters
(usually  every port is in/out capable )