I hate to answer like this but, there is just too much to type. So check out:
http://www.photographyboard.net/the-use-of-filters-
355.html
It's written by a board member and will explain the basics of color filters, different types of filters and how they attach to your lens.
For more specific info on B&W filters you can download a PDF file from Schneider Optics:
http://www.schneideroptics.com
choose: still photography/literature/black and white filter handbook.
For landscapes I generally use: yellow, orange, red, green, Neutral Density or a polarizer.