You register your number or email address and city. They then send you details on the next sighting of the International Space Station.
The station is the third brightest object in the sky just after the sun and moon. So you can see it without a telescope with your naked eye...preferably not naked.
http://spotthestation.nasa.gov/
The notification looks like this:
I have yet to see it. It passes in view at around 8 pm and 6 am.SpotTheStation! Time: Tue Nov 06 4:17 AM, Visible: 6 min, Max Height: 46 degrees, Appears: SSW, Disappears: ENE