Hanuman Bhauk is an important prayer dedicated to Hanuman and was written by Goswami Tulsidas. It is believed that Tulsidasji wrote to prayer to cure his shoulder pain. Once, Tulsidas had an excruciating pain in one of his shoulders. He then composed a poem extolling the glory and greatness of Hanuman. He also asked Hanumanji to cure his body ailments. Miraculously Tulsidas had relief from the pain.
It is believed that chanting Hanuman Bahuk helps in curing various body pains, diseases, psychological problems, fear of ghosts etc. It is also chanted by those people who believe that their enemies are doing black magic against them. A person can chant Hanuman Bahuk daily as part of his normal prayers. Another method of chanting Hanuman Bahuk is by doing certain austerities for 40 days. On all forty days, Hanuman Bahuk is chanted in the morning. The person only eats vegetarian food. No smoking and drinking during the period. No gossips and no unnecessary talks. Chanting the Stotra is also believed to help in wish fulfillment.
(This was taken directly from Hindu Blog.)