A bibliography is an overview of (almost) all publications in some category:
works of some author
publications about some specific subject
publications published in some specific country
publications published in some specific period
publications mentioned in, or relevant to, a particular work (a bibliography of this type, sometimes called a reference list should normally appear at the end of any paper in scientific literature)
A bibliography tries to give a complete overview of the (important) literature in its category. This is opposed to a library catalog, which only describes items actually found in the library. However, some national libraries' catalogs also serve as national bibliographies, as (almost) all publications of this country are contained in the catalogs.
Bibliographies can be sorted in several ways, similar to library catalogs.
Annotated bibliographies give descriptions about how each source is useful to an author in constructing a paper or argument. Creating these blurbs, usually a few sentences long, establishes a summary for and expresses the relevance of each source prior to writing.
Bibliographer is the incredible new program that will generate bibliographies in standard MLA format in a simple and easy to use interface.
Bibliographer previews exactly what your bibliography will look on paper at all times, so you'll never have to guess on your bibliography's final appearance on paper.
Bibliographer lets you change the way it generates bibliographies allowing you to decide if you'd like it to double space the entries, number the entries, or even indent each entry's subsequent lines.