Transparency in computer graphics refers to the ability so see through an item - either partially of fully. The term Translucency is used when light can pass through, but you cannot see throught clearly.
There is "full transparency" i.e. something that is completely invisible. Of course, only part of a graphic could be fully transparent, or there would be nothing to see. And there is "partial transparency" or " translucency " where the effect is like colored or frosted glass.
Videos and Tutorials
Transparency may be stored in a raster image in an Alpha-Channel (α-channel). This is an additional channel in digital pictures, which contains, beside color information, the transparency (how much you can see through an object) of each pixel in an image.
You can also make an object of face transparent by giving it a transparent material.
You can select a predefined SketchUp transparent material from the SketchUp Material Browser, such as this glass:
, or you can create a new transparent material, (or edit an existing one), by defining its opacity.
IRender nXt Transparency Adjustments
IRender nXt makes some adjustments to SketchUp transparency to try to make the transparent faces appear more like they do in SketchUp.