Step 2 - Download StepMania: SourceForge StepMania page.
Scroll down the page (feel free to look around!) and click on "View ALL Project Files". Select the latest version for your PC platform (such as "StepMania-3.9-rc2a.exe"), follow the download instructions and read Beverly's helpfile.
The Stepmania-game is usually played using the computer's keyboard, but using a dance pad or a controller are popular options (see picture below).