1. (G)ross (V)ehicle (W)eight (R)ATING or GVWR is the maximum weight the vehicle is designed to carry safely/legally.
2. A TRAILER IS A VEHICLE.
3. No vehicle should exceed the GVWR – period. It’s unsafe.
4. (G)ross (C)ombined (W)eight (R)ATING or GCWR = GVWR of the truck PLUS the GVWR of the trailer.

Example:
Ram 3500 pickup GVWR = 11,700 lbs
PJ trailer GVWR = 10,000lbs
GCWR for this combination is 21,700 lbs

Which means, under no circumstance can the truck be heavier than its GVWR and neither can the trailer. That includes the actual weight of the truck with driver, fuel, passengers, and trailer tongue weight (how much weight the trailer adds to the truck) can’t exceed the GVWR for the truck. Additionally, the trailer (actual weight on its axles) can’t weigh more than the GVWR of the trailer.

The example truck might weigh 9000lbs empty, add all the other “stuff” ( people, luggage, dogs, kids etc) and a full tank of fuel it might weigh 10,000lbs (well below its RATING of 11,700lbs).
Then add the weight of the trailer tongue (about 10% of the total trailer weight) say its fully loaded, so that would be 1000lbs of tongue weight. Now the actual Weight (GVW) of the truck is 11,000lbs. Still safely under the RATING of 11,700. The trailer and its load weigh 9,000lbs, still safely under the weight RATING for the trailer. This is an acceptable combination, all good.
The Gross Combined Vehicle Weight or GCVW (not the RATING, the actual weight of truck and trailer) is 20,000lbs, still well below the (G)ross (C)ombined (W)eight (R)ATING for this combination. Essentially the manufacturers of the truck and trailer have certified this combination to be safe to operate on public roadways.

Hope this helps
Cheers!