Skill Saw With Saw Guide
As you can see in this picture of the saw ripping a 2 x 6
from a 2 x 8 the saw guide helps to keep the saw Straight in the result
will be a nice Straight board. The saw guide is not the necessity to
building a set of stairs. You can use an alternative such as a Straight
edge or a chalk line.
This picture gives you a nice upper view of the saw guide being attached to the saw.