The cable jack at most marinas is just like your cable TV at home. Connect a cable to that jack then to any TV and you should get TV pictures. What you get is dependent on the marina's cable plan, usually basic but that will give you all of the local channels.
A smart TV or a non smart TV with a Roku box or similar will let you stream TV from Amazon, Netflix, Hulu, etc. This requires a pretty fast wifi connection. This can either be from your marina (usually pretty slow) a nearby Xfinity or similar hotspot, a cell phone hot spot, etc. The cell solutions eat up data pretty fast if you stream TV.
One new system is TOGO, a $400 Wineguard antenna with a $360/yr. ATT unlimited data plan. Yes really unlimited. Check out the reviews on the RV web sites. It is getting pretty good reviews. My buddy just installed on on his RV a few days ago. So far, great.