Before pouring concrete steps coat the forms with a release agent.
How to form concrete steps with side walls.
Then pour your concrete inside the form using a chute or hose attached to the mixer.
If your not sure what that means its simply using a discardable material inside the box to make the sidewalls the desired thickness.
Assemble your concrete form.
Building formwork when forming between walls or other flat surfaces such as plywood where you will be able to mark riser locations positioning risers is easy.
The inner side wall form would be your tricky cut but could be braced one to the other.
A cap on the wall would be needed and you would want a thin mix on the wall but a thicker mix on the steps that you would pour first.
A monolithic pour would give you the best outcome.
If steps are longer than 4 feet install stringers to support risers and keep stair lines straight.
You can do it like a wall build a wall set your risers and false form the inside of it.
Keep in mind though that if the finished exposed product is going to be concrete you ll need to strip all of this out finish it all before the concrete sets completely.
You would cut a form for the inside that would be similar to a stair stringer but set upside down.
Tap the sides of the forms and risers with a hammer and jab a 2x4 up and down in the mix to drive air bubbles out.
Set riser boards to the marks and fasten them to the walls or side boards.
Shovel the concrete inside the forms starting with the bottom step and working up.
The form for the exterior of the wall would be far simpler.
Mix the concrete and bring it to the site in wheelbarrow loads.
To make the wall as strong as possible pour the concrete in layers no higher than 20 inches working from 1 end of the wall to the other.