A stair ladder is a multi-purpose combination ladder that has a variety of uses, one of which can be used on stairs. To use a combination ladder on stairs you should change the configuration to an A Frame and rest one side of the ladder on the stairs with the other section on the landing space below the stairs. When purchasing a stair ladder be sure to check they are suitable for use on stairs, some of the larger sizes can be unsafe to use. You can check how to use your specific ladder on stairs in the user instructions.