Hi there.
It`s very easy. Do the following:
1. After selecting the tool, observe that you can drift: Run, Boundaries or Risers; If you want a ladder with the same width all along the way, you can choose Run; If you want a ladder different (as shown on this example, you`ll have to work with the two other options);

2. You have to know what`s the level you want to reach; Check the properties pallete to set the base and top levels such as the width of the ladder and the desired number of risers;

3. First, start drifting the boundaries. Observe that the boundaries are green lines, which are going only on the side of the stairs. Second, start drifting the risers. Every gap between two risers is a tread deph, so observe: if you set 1 meter between two risers, for example, you`re doing a landing;

If the message below didn`t say 0 remaining, you didn`t reached your pre-selected level. Revit will let you do this, but will warn you; It is necessary that the risers lines be drawn exactly between the boundaries lines, just as shown;
4. After adjusting your number of risers until the massage say 0 remaining, you`re all set. Just confirm the ladder and check the result. In case you want to change something, select it and click on Edit Skecth. If the up direction isn`t right, select the stairs and click at the arrow to flip it.

If your problem has been solved, please click on Accept as Solution. Then others users can take benefit of it.
Regards,
Felipe Góes
Autodesk Instructor