How do I know which keg post to put the regulator assembly on and the faucet assembly on?

On the keg you’ll see an IN post (male fitting) and OUT post (male fitting).  Black = booze.  Booze goes OUT.  Gray = gas.  Gas goes in.  Be sure to pull up on the collar on the disconnects (female fitting) and push down until you hear the distinct CLICK of the poppet and disconnect engaging properly. Make sure to keep the o-rings on the keg posts lubricated with food-grade lubricant!