Blender is able to "reach in" to other .blend files and pull in whatever you want. In this way, Blender supports reuse of your graphical models. For example, if you have a library .blend file that has a really neat Material used in it, you can, from your current .blend file, Append that Material into your current .blend file. This saves you from manually re-creating all the different settings.
Texture plugins are external files that can be loaded up in the Blender interface, which provide controls in the Plugin panel based on what they can do. A plugin texture is a dynamically loaded library that exists as a separate file on your computer. When called in, it generates the texture.
While rendering stills will allow you to view and save the image from the render buffer when it's complete, animations are a series of images, or frames, and are automatically saved directly out to disk after being rendered.
This tutorial is meant to explain in consecutive steps exactly how to take one of your really neat 2D images you created in a program such as GIMP and attach it to an object you will create in Blender (in this case you will create a plane).