To train means to teach a skill. If you train your cat to use the toilet, your family will be amazed.
You can train animals to perform in a circus or roll over, and you can train people to do things like program computers or use an espresso machine. When you instruct someone how to do a task, you train him or her. Other meanings of the word train? A locomotive, like the train that takes people from New York City to Boston or a long piece of material attached to the back of a dress, like the train on a wedding dress.