once you've got your risers you'll want to notch the bottom for a 2x4 if your building indoors to code. This is most easily explained by a diagram. see below.
Now you want to attach the top of the riser to the structure you want to access. place the final rise against the front surface and screw in with hangars. place the second riser the step distance apart and screw in with hangars. place any additional risers in between appropriatly.