Do you know how to qualify prospect tenants? Are you aware of Federal and State Fair Housing Laws that landlords must abide. Do you want to manage the tenants' needs after they move in? Will you be avaialbe 24/7 for repairs and for emergency services? Do you want to collect the rent? The answers to some of these questions will help you to decide between a property manager or a Realtor.
In general, property managers charge a monthly fee - 10% of the rent amount, or a fee for service schedule.
If you choose to work with a Realtor, then I suggest that you discuss with the agent and agree upon the responsibilities: (partial list only)
1. Research and qualify the tenants
2. Frequency of showing the property to prospective tenants
3. Records keeping for Fair Housing Laws (in case of any legal issue) http://www.hud.gov/renting/tenantrights.cfm
4. Preparation of the rental contract
5. Review rental contract with tenant and disclose tenant rights, landlord rights
6. Discuss rules for tenants, if any. Parking, repairs, maintenance, smoking/non-smoking, pets, etc.
You should be able to find such companies in your local phone book and I would recommend interviewing more than 1.