If you're in an urban area, Google will normally be able to get your exact location from the street address you added, provided you included your postal code.  But sometimes the results are way out.

If the marker position is reasonably close to accurate, click the Map it button to open your map, and then drag the marker to the correct position.  Enlarging the map and changing to Satellite view will help you position it accurately. And then close the window.

If the marker is in the wrong place completely, click the Clear coordinates button to clear the GPS co-ordinates, and
either try to improve your street address, maybe adding more details in the street address field such as town name (if the marker got your town wrong), and then click Map it again.  You can also just drag the marker to the correct position, after changing the map's scale.

If you have GPS co-ordinates, you can add those to the latitude and longitude fields.  Just make sure that they are in digital format (see next question for help) and that you include the minus sign for latitude (for the southern hemisphere).

Google Street View
It is exactly what it says: a street view outside your location rather than a picture of your location.  To look at the properties on either side of a position, one needs to turn the circular orientation tool clockwise or anti-clockwise.

When you move the marker, the position of the street view changes too.