It all depends upon what
type of material you're going to use for your stair risers, whether you
can use a circular saw or not. However, a circular saw will cut most
construction standard lumber and engineered building materials.
You can also use a table saw or attach a saw guide, to your circular saw, to increase accuracy.
If you haven't ever used a saw guide before, be careful. If you're going to make consecutive cuts, in a row, you will need to check every other cut, to make sure that it's still Straight.
When I first started using saw guides, it took me about a year to get used to them.
Plywood And Oriented Strand Board RisersTo make things easy, layout and mark one riser and then use that one as a template, to mark, layout and cut the rest of them.
After you have installed your stair stringers you can measure the width of the risers and then cut them accordingly.