Portable steps are usually made from wood, such as plywood. Wood steps provide adequate support for the average person's body weight and can be made with minimal equipment, such as wood, nails and a hammer.
You can purchase pre-cut steps from your local hardware store. There are plenty of resources available to serve as a guideline for building your steps, if you're not sure about how to put them together.
Wooden steps need to be treated with a strong wood finish. This will help them pass the test of time. For additional safety, glue treads onto the steps to ensure that your feet are firmly balanced and that you don't slip.