To draw perspective stairs in Photoshop, start by creating a new document where you would like to draw the stairs. As a next step, to set up the grid, go to the 'view' option from the menu section, choose 'show', and then select 'grid'. This will help you in aligning the objects in a proper order. Now, choose the line tool and draw a straight line that will represent a horizon. It is an important step as it will determine the eye level and the perspective. Now, add vanishing points to the horizon line. These are important points that will determine the direction of the stairs. After you have established the vanishing points, draw lines extending towards the bottom portion of the canvas. With the help of these lines, draw rectangular boxes for each step. It is important to ensure that the rectangles should seamlessly follow the perspective lines and they should start diminishing in size as they begin to disappear. With Photoshop, you have the flexibility to enhance the overall look of the stairs by adding details like railings or textures.