All you have to know is your location (usually, the website finds you automatically) and clear sky.
The most popular watch is the ISS, which is sometimes very bright and in the sky it goes from west or south-west.
The ISS is a project of several space agencies: the American NASA, the Russian Federal Space Agency, the European ESA, the Canadian CSA and the Japanese JAXA. The ISS is at an orbital altitude of 330 – 410 km. It completes 15.7 orbits a day.
On this page, click on the satellite you want and open the time schedule of passes in your place.