The first step is to choose a command for your dog to sit. The most common command is "sit," but you can also use "stay" or "down."
Once you've chosen a command, you need to get your dog's attention. You can do this by calling their name, clapping your hands, or making a noise with a clicker.
Once your dog is paying attention to you, hold a treat in front of their nose and slowly move it up over their head.
As soon as your dog sits down, mark the behavior by saying "yes!" or clicking a clicker. Then, give them the treat.
Once your dog is consistently sitting on command, you can start to fade out the treat. Start by only giving them the treat every other time they sit.
Once your dog is consistently sitting on command in one location, start to practice in different locations.
Training your dog to sit takes time and patience. Be consistent with your commands and rewards, and your dog will eventually learn.