The question's a bit vague. If you're referring to distributing weight once you're loaded, it depends on what your trailer has for axles. If you have fixed tandems or a fixed spread axle, you would have to move the load itself. If you have sliding tandems, you can move them forward to shift weight from the drive axles to the trailer axles, or you can move them back to shift weight from the trailer axles to the drive axles. If you have a sliding fifth wheel, you can move that forward to shift weight from the drive axles to the steer axle, or you can move it back to shift weight from the steer axle to the drive axles.
There is no minimum weight.
Most trailers are semi trailers. You're probably asking the difference between a semi trailer and a full trailer. A semi trailer is not wholly self supporting, and weight is distributed both the trailer axles, and to the tow vehicle. A full trailer supports its own weight fully.
The weight capacity for semi trailer is 80,000 LBS. That is calculating with two or more consecutive axles to the nearest 500 LBS.
The "tractor" is the vehicle which actually powers the combination. A semi-trailer is any trailer in which the weight of the trailer (and the payload) is shared between the trailer's axles and the axles of either a dolly or the towing unit (in contrast, a full trailer supports all of its own weight).
As evenly as possible between the drive and trailer axles.
A semi trailer is any trailer which doesn't fully support its own weight. That's the ver batim definition. A boat trailer for private use is not regulated the way a commercial use trailer is.
Bottom hopper grain trailer.
The load on the king pin on a semi trailer can be calculated by weighing the vehicle. When weighing the vehicle on a certified scale, the steers (front tires), drives (the two axles on the semi cab) and the tandems (the two axles on the trailer) are all weighed separately as a part of the whole weight. The king pin weight is the weight of the drives.
14,000 lbs
You have to put your weight evenly between your trailer axles and your trucks rear axles. You have to know the weight limit of your truck and trailer, it should say in the owner's manual or you can read the weight limit on the tires. The majority of the weight should be on the trailer because if you put most of the weight on the truck the trailer will begin to fishtail. If it is a flatbed trailer and you look along the side you will see that it bows up, you should never load it to were it bows down because it is probably overloaded at that point. Also you should read the owner's manual to learn how to move the axles on the trailer.
69,500 pounds
truck and trailer 35000 pounds.