A horse is naturally inquisitive and determined to explore their environment and enjoy it! You will notice they are constantly moving their feet every 3-5 seconds when grazing. When stabling a horse you may want to perform many of their natural behaviors in their new environment for them, for certain reasons.
Without naming many things you can do yet, spend some time with your horse and see if you can develop a personal bond where you guys can communicate. When your horse is on a comfortable level with you, play some games with your horse, hide food in the hay, or tie some kebabs on the post for your horse.