Be more specific, whats wrong with the concrete your trying to repair. Any pictures?
Slab...foundation, piers, steps, patio slab, driveway, retaining wall, bird bath?...concrete is a widely used product. What the intended purpose is will dictate how or what repairs are needed.
A lot depends on how serious the damage is and what exactly is damaged. If the damage is on a major component of your house, like the foundation, I would definitely hire a professional. There are tons of services out there that are specialized in concrete repair. Just be sure to do your research before hiring a service. Good luck to you! http://mararestoration.com/maraservices/