It depends on the stallion. All the breeders I know, pasture breed. It is more natural. If the stallion is too young, he will chase the mare, nip at her heels, and so forth. Then, he is not ready to breed.
When he is ready, the first time he mounts, he will probably try and mount her from the sides before he figures out where he is supposed to go.
The mounting from the side is hilarious to watch, you do need a good old mare for a youngster to practice on. The mare will look bored, the stallion will look *very* confused. :-D Most mares, even young ones, will not allow a stallion to harass them. Arabians are highly domesticated horses, they have lived *with* people for centuries, I would expect, like Lusos, most of the bad breeders, that is, the foal killers and the rapists, have been bred out.
The thing to do is just put them together for a day when you can watch. If, after the initial excitement, they settle down and graze together, they will be fine. If after 4 hours, they are still running around and getting very stressed, it is probably not a good idea. Most good stallions only cover a mare when she is season, so with a fertile mare, the stallion gets one go in exchange for a year of care and protection!
Here's a vid of my stallion running with four of my mares. My neighbours who can see the field from their living room, reported that he had "a busy couple of days" - then it stopped. So I hope they are in foal!
His first season, he was just turned out with one mare, and not only did they get along fine, but she is still his best friend, they really like each other, and I have seen her put herself between him and another mare that was lashing out at him. This is him and her.