You see a cute puppy. You fall in love and bring him home. Every little thing he does is so adorable, until he chews your favorite shoes into shreds. That is when you might call a pet trainer.
There have probably been pet trainers about as long as there have been pets. Like people, animals have different personalities and young animals are kind of like children in their development. Some times they have to be taught how to behave. That is where pet training comes in.
A pet trainer can help if your dog barks excessively, or is aggressive, or has other issues. Some dogs jump on people, furniture and other objects. Dogs like to dig, and have been known to dig up flowers and vegetable gardens. They knock things over, break stuff, drool and are famous for chewing things that they are not supposed to. Most dogs, especially puppies, could use some kind of training.
Dogs have been taken to trainers at obedience schools for behavioral issues for many years. More recently, they have also been using online pet trainers. There are many different websites that offer advice on how to train your pets. Many of them have video instruction, and make it easy to train your pet without having to leave your home.
Training is not just for the dogs. While they are generally easier to care for than dogs, cats can be trained too. Kittens need to be trained on how to use a litter box, and some cats need to be trained to stop scratching things like furniture. There is online pet training available for both dogs and cats.