With their medium to long, fine, glossy coats, these dogs will need a good bit of attention, so overall Gordon Setter grooming is a fairly time-consuming process. Gordons' coats shed a good bit and are prone to tangles and mats, so they'll need to be brushed 4-5 times per week; because their coats are glossy and shiny, they also need frequent baths (every 1-2 weeks). And though most Gordon owners don't give their dogs fancy hairstyles, these dogs will need their coats trimmed every couple of months.
Brushing a Gordon is best done with a pin brush, and it'll probably be good to have a slicker brush or 2-in-1 comb handy for working through mats and tangles. (A leave-in conditioner or de-tangler spray will be nice to have as well.) To brush a Gordon: first wet the coat with mist from a spray bottle (mix in some conditioner/de-tangler if desired), then use the pin brush to go over the coat in typical line-brushing fashion. If you're following the brushing with a bath (which should happen every week or two), use a bathtub or outdoor kiddie pool with a garden hose. Make sure to use canine shampoo and conditioner, as this will help the coat retain its shine. Lather and rinse well, towel-dry, then give the coat another quick brush-through to make it look healthy and clean. In between baths, you can also spray the coat with the leave-in conditioner when you brush to help the hair keep its glossiness.
Giving a Gordon Setter a trim every 6-8 weeks is a good idea, for several reasons: not only will a trim minimize tangles and mats, but doing so will remove dead/split ends, further aiding in the coat keeping its signature gloss. Many Gordon owners learn to trim their dogs' hair from instructional videos on YouTube or other sites, but it might be good to have a professional groomer do it at least once; the groomer can show you how to trim your dog's hair yourself, and can provide advice on grooming Gordon Setters in general.