I worked in behavior health for 23 years first as a practitioner and then as a CEO.
"Obsessive Compulsive Disorder"
Obsessions are resident in a person's thoughts. They cannot stop thinking about an object or an event. Thoughts like "Are my hands clean enough?" "Did I forget to turn off the stove?" "Will I be found to be a fraud at my job today?" etc.
Compulsions are behaviors that a person feels they must complete before moving on. Technically, these behaviors must also diminish a person's quality of life: turning off the stove 10 times before believing it is off, checking the expiration of food multiple times before eating it, locking the apartment door many times over before leaving, etc.
Triggers are atypical stressors or typical stressors that increase in severity and frequency.
Yes, people can be delivered from it. The disorder has its roots in fear and self-protection. Often you will find a traumatic event, or a series of events, that formed the person's disorder. Medication can help with the symptoms but not with the root of the trauma.
How to pray depends upon how much you know about them. Pray for peace (the destruction of chaos) and for understanding and for healing. Conventional therapy will help them cope but only the Truth will set them free.