There is usually two ways the SHORE POWER CABLE works with the trailers.
One is a small door that opens on the outside of the trailer and you find the 30A Power Cord plug you can pull out for about 25-feet and plug into the camp ground ground 30A Power Pedestal

Your 30AMP Plug on the end of this cable will look something like this

Other trailer may have an 30AMP RECEPTACLE on their trailer to hook-up to and use a RV 30AMP Shore Power Cable 25-foot extension cable. The receptacle on the trailer will look something like this...

The RV 30AMP SHORE POWER 25-foot Extension Cord will have a TWIST LOCK 30AMP connector on the trailer end and the standard RV30AMP Plug on the camp ground pedestal end..

The camp 30AMP pedestal look something like this



A typical Camp Ground Pedestal is wired like this...

Roy Ken