The skill to quickly view a object from a particular angle and distance, is a most important skill in building. It is not just useful in building, but gives you much power when playing Second Life, allowing you even to view past walls. Practice viewing throughly and it will save you much time in building.
The Focus button lets you view a object from various angles. Note that you can invoke the Focus mode by simply holding down the Alt key. (or Option on the Mac). You do not need to bring this build dialogue up.
In Second Life, what you see on the screen, came from what's called a camera. This camera has a position, direction, and orientation. Normally, it trails 3 meters behind you and 1 meter above your head, and is pointed towards in front of you, with a orientation that's the same as your upgright body. So that, you constantly see part of your head and shoulders from the back, and scenes in front of you.
Second Life allows you to change the position and direction of the camera freely, independent of your avatar. If you are skilled, you can manipulate the camera as to follow a path, allowing you to view into corridors. In effect, it's like you have a remote controlled floating camera that you can send to snoop things while you standstill. (There is a limit on this. Your camera cannot be further than ~10 meters away from your av. So, you can't spy on your friends thousands miles away.)
Here are descriptions on how to control your camera. These techniques can be used while building too:
• To zoom in/out: hold down Alt, then click (and hold) on the object of interest, then move your mouse forward/backward. (If you want want to zoom in the center of your screen, then you can just use your scroll wheel.)
Note that zooming in/out is just moving your camera forward/backward.
• To orbit your camera left/right around a object: hold down Alt, click (and hold) on the object of interest, then move your mouse left/right.
• To orbit your camera up/down around the object: hold down Alt and Ctrl, then click (and hold) on a object of interest, then move your mouse up/down.
• To pan the screen (meaning: moving your camera down/up/left/right but without rotating your camera): hold down Alt and Ctrl and Shift, then click (and hold) anywhere on the screen, then move your mouse down/up/left/right.
The camera can also be controlled using just the mouse. Select the menu “View:Camera Controls” and you'll get a user interface pane.
above: The Camera Controls user interface pane, from the menu “View:Camera Controls”. The left circle orbits the camera around the object (tilting the scene up/down/left/right). The middle ruler controls forward/backward movement (zoom in/out). The right circle controls up/down/left/right movements (panning the screen).