Not in the same way that you ride a horse. They can easily be trained to carry a saddle, but normally they still have to be led with a lead rope. We often will put a young child on a llama for a parade, but that is one of the few occasions that anyone rides any of our llamas. They are strong enough to lift an adult, but they are usually smart enough not to try to carry one. If the load is too much for them, they will often just lie down and refuse to go anywhere until the load is lightened.
Llamas learn very quickly.
Usually by the time they have repeated something about three or four times, they have it learned. Once they overcome any nervousness, they are very easy to train, and once they learn to trust you, they will follow you anywhere. Many people train their llamas to climb into a van, which certainly makes it easier than hooking up the trailer anytime you want to take them somewhere. Llamas normally will lie down when travelling so you can safely carry them in a van or in a pickup with a canopy. If our llamas are going to be in a trailer for any period of time, what we do is get a small coffee can and put some fresh droppings in it.