There are two ways
Google Maps from the web browser and Google Earth from the desktop can view Street View. you can also view traffic.
Google Street View is a technology featured in Google Maps and Google Earth launched in 2007.
In Google Earth v6 you drag the new orange "pegman" icon (found near the navigation controls) onto the map to enter Street View. As of Jan 2012 Google has discontinued Street View support in Google Earth 5.2 and earlier.
by google map or google earth
When Google updates it street view photos in its image database then these updates are made available to Google Maps and Google Earth.
on Google earth but you have to download it first
Here is one of Google's announcements of ending Street View support for Google Earth versions 5.x and older. "With the most recent update to Google Earth (6.2), we are also finalizing our transition to a new method of delivering Street View imagery in Google Earth. This means, that the older versions of Google Earth (anything before 6.0) will no longer be able to access Street View. We held off making this change until now, when the vast majority of Google Earth users are on 6.0 (or later)." -- Google Jan 2012. Basically, Google decided to improve the Street View interfaces which would be implemented in the current versions of Google Earth for desktop and mobile platforms rather than keep supporting the older (less efficient) method of accessing Street View.
Street View, google's high-res panoramic view, can be enabled in Google Earth v6 by dragging the orange "pegman" icon (found near the navigation controls) onto the map.
You can, but it is a rather new functionality added to Google Maps / Google Earth, and at the moment, the street view is only available for major avenues and roads.
To compile Google Earth street view photos, Google send out vans with panoramic cameras. Because it was and is an huge task, some images are not up to date, but it is an ongoing process.
Not yet for Google Earth. Google recently created historical imagery for Street View on Google Maps. If historical imagery is available then a clock and date will be displayed in the upper left of the map.
Accessing Street View depends somewhat on whether you're using it from Google Maps or Google Earth.Street View in Google Maps:Drag the orange "pegman" icon from the navigation control (on upper-left corner) onto the map to enter Street View mode. If blue lines appear on the map then those lines indicate where street view is available [not all areas have street view].Street View in Google Earth 6 and 7:Drag the orange "pegman" icon from the navigation control (on upper-right corner) onto the map to enter Street View mode. Also if you're looking at ground from low altitude then double-click on a building or ground to enter nearest Street View photo from that location.Street View in Google Earth 5:Check the Street View layer under Layers panel then double click on photo icons that appear on the map.For tips to navigate in Street View see related links for video tutorials.