The ISS orbits about 250 miles above Earth, which is why a 5-watt radio can be used. Without a repeater, a 5-watt signal typically reaches a distance of only 5 miles (Source: I tested).
If you are looking to learn how to set up the radio, the manual is the best resource. As @WSDM599 mentioned, if you want to learn about different types of radios, Amazon offers several books on Baofeng and other radios.
I have tested the Watts L2 M5 H10, and this radio is FCC part 95 certified. It works great with a GMRS antenna. I will give it a rating of 10 out of 10.