You wouldn't want your dog running with another animal that may physically injure him or frighten him. The dogs should be so intent on the lure that they don't even pay attention to other dogs. By testing the novice dog with an experienced dog that is known to be a clean runner, in the presence of a judge or someone in an official capacity, there is some guarantee that the animals are safe. Most clubs have someone on hand at a practice to test the dog as a clean runner. Once this has been accomplished, you're ready to enter your hound in an official trial.
Information is given as to the individual club's entry policy.
Read the instructions carefully to discern the difference. The premium lists are available at various conformation shows and other trials prior to the event. Most clubs have a mailing list for those who wish to be sent premium lists for their trials. On the day of the trial you must be in attendance with your dog at roll call or you cannot participate. It is advisable to bring everything you will need for your dog to be comfortable for the duration of the day.