For your artist, the place to begin is with a Disney or similar book on traditional animation which teaches what frames are, the principles of squash and stretch, and gives examples of walk and run cycles. Muybridge's photobooks of humans and animals in motion are also great resources. Tool-wise it's best to have a light box, a scanner, a printer, and a quality image-editing program. You can test simple animation sequences by animating just the lineart as an animated gif (gimp is one free program which can do this). Then when this 'pencil test' looks good you color and finalize each frame to create one of that sprite's animations. A sprite is basically one character or monster doing all the motions you want it to do in the game.

Making a sprite depends on your game engine, some use strips of images stuck next to another, some use grids, some use animated gifs, separate numbered images, Flash movieclip or other formats.

What you WILL need is animations, say, a walk cycle. You will need to draw each frame and output it to your engine format. There are great books on animation such as Animator's survival kit

or The Animator's Workbook: Step-By-Step Techniques of Drawn Animation