01
The terms
Gross weight is the maximum permitted trailer mass. Empty weight is the trailer without cargo. Payload is roughly what you can add. Actual loaded weight matters when you drive.
02
Towing capacity and tongue load
Towing capacity is the car's limit. Tongue load acts on the coupling and affects stability. Both limits must be respected even if the trailer still has space.
03
Practical rule
Load heavy items low and near the axle area. Secure loose goods, add up weights and choose a lighter setup if unsure.