There are 3 major types of graphic files: Raster(Bitmap), Vector(Object), and Other(Metafile).

Raster files are commonly referred to as bitmap files and primarily created from paint programs, scanners, and digital cameras. The pictures are made from a grid of dots called pixels which create the image.

Vector Graphics (also called object graphics) store image information mathematically as a set of objects, lines, circles, arcs etc. They are primarily used in engineering fields, professional printing, and animation.

Most of the files in the 'other'(metafile) category are files that either use a combination of both bitmap and vector information, or are used to create graphics which will later be saved in one of the two formats. The Photoshop format is a file that contains multiple image layers which can contain vector or raster information. Likewise microsoft Clipart may contain vector and/or raster information.

Some common file formats include:

Studio Max
Paint Shop Pro

If you just want some quick notes and comments about graphic file formats
read the support section "File Formats Quick List".
Quick File Format List

Next -----> 2. Bitmap and Vector Graphics