Redd is a fox that comes into your town every week at one specific day that will sell overpriced items in his tent. Most of his items are just general items you could get at Tom Nook's but he does sell sometimes rare and Redd exclusive items that will have an HRA bonus. Check an item list to see if it's an exclusive item. For the main part, try and stay away from his merchandise unless you really want an item or if it's a rare item.
Redd is associated with Lyle the Insurance salesman. If you haven't met and talked with Lyle yet, Redd shows up on a random day of the week. If you do talk to Lyle and buy insurance, he'll let you choose when Redd comes into town. Then, Redd will come into town every week on that day until you change it.
To enter his tent, you'll need a password. The first time he comes around, you'll need to talk to your animal villagers to find it out. You can enter the tent now by entering the password, and then Redd won't allow you to buy anything because you're not in the family, which you can conveniently join by paying a one time fee of 3,000 bells. After that, you can buy from his shop and you'll get the password by mail every week before he comes.
Redd's prices are high, you can find the furniture at Tom Nook's, but the paintings are only at Redd's. Some of the paintings are not real, Blathers will tell you if they're fake.In order to avoid fakes, sell your painting to Tom Nook immediately after buying it, then order it from your catalog. voila. Instant genuine painting!
~Sometimes Tom Nook will spot a forged painting and pay barely anything; the real painting won't show up in the catalog if he does this.