The International Space Station (ISS) is a manned space station that is operated and expanded in international cooperation.
The first plans for a large international space station were in the 1980s under the name Freedom or Alpha. Since 1998 the ISS is under construction. Currently, it is the largest artificial object in Earth orbit. In about 400 km of altitude, with an inclination of 51.6 °, it orbits about 92 m in an eastern direction around the earth and has an extension of about 110 m × 100 m × 30 m. Since 2 November 2000, the ISS has been permanently inhabited by astronauts.

You can observe them as well as other artificial objects in the sky with bare eyes
Use here for the app Heavens Above It is available in  GooglePlay store. With this app you can see all satellites and, of course, space stations in the sky.
ISS is a very fast and bright moving point.

With a good telescope you can even see the outlines of the ISS.