To connect to your Slingbox using Watch on Slingbox.com, simply connect the Slingbox to your home network, and use Watch on Slingbox.com to configure it. The Slingbox is automatically added to your Sling Account profile and to your Slingbox Directory. This works similarly using Slingplayer for Desktop.
If you have an older Slingbox, you can alternatively add the Slingbox to your Sling Account profile manually by specifying its Slingbox ID. To find the Slingbox ID, take a look at the article below. When you have the Slingbox ID, you can go to the Sling Account page and add the new Slingbox to your profile.
If you're using a Slingbox M1, Slingbox 350, or a SlingTV/Slingbox 500, you no longer need to concern yourself with the Slingbox ID. But if the automatic router setup doesn't work for you, the article linked below provides additional help connecting your Slingbox.