Where do you install ADSelfService Plus

Where do you install ADSelfService Plus

So this is a super simple question but for some reason I'm not understanding how ADSelfService is installed

  1. Do you install the Software on your domain controller/some other server and clients access the web portal?
  2. or Do you install the software on every client's machine? 
Option two doesn't seem right, but I can't find instructions explicitly saying to install the software on a server.

Thanks.