Google Street View is a subsection of Google Maps. It shows you the actual view of a particular street all the way up to the Moon or even other planets.
Google had a lot of vehicles equipped with cameras that drove around most of the streets and highways in the United States and some other countries. These cameras caught a snapshot in time of all the roads traveled. Sometimes they caught funny things like dogs pooping on someone's lawn or even some folks having relations in public.
All one has to do is use Google Maps to find an address and click the "street view" option. You can see if the house you used to live in is still there and painted a garish purple.
Google's street view option is incredibly helpful for writers. Normally we're toiling away but we need to see what's on a particular corner in New York City because the characters are about to get ambushed. Using GSV you can discover there is a pizza joint on the corner, a metal electrical box, and a public mailbox. You can have the characters shoot it out while hiding behind things that are really there, which will make it appear to your readers that you traveled to that corner to make it as real and accurate as possible.