The single most important consideration in choosing a knife for whittling is that it fits comfortably in your hand. A locking flip blade or a pocket knife with a sharp steel blade suffices for beginners; avoid stainless steel however, as it dulls quickly and is difficult to sharpen evenly. Special whittling knives can be purchased from most craft stores either in kits or alone. Their handles are short and rounded for easier gripping and maneuverability and you may want to make the investment as you become more adept at whittling.
You can purchase wood from a lumber yard or home improvement store; you might also ask the manager for scrapes from the trash bin to get started whittling. Look for soft or semi-soft wood like pine, balsa or cedar; make sure your wood is uniform in color; darkened spots indict variation in hardness. You may also choose a small green branch that has recently fallen from or been pruned from a tree in your own yard. Ensure it's fresh; dried branches harden and are more difficult for beginners to work with.
Grip your knife so your thumb is placed along the spine and the edge faces towards your fingers. Hold your wood in the other hand so that the end you intend to start working if facing away from you. Position your elbows close to your sides and lock your wrists. Lay your knife against the wood with the blade facing away from your body. Slice downward to make your first cut and repeat to shape your wood as desired. Once you are comfortable whittling, you can create items from your own imagination or use whittling patterns, like the little bear, to spark your creativity.
Use a soft cloth to clean wood shavings from the blades and crevices of your knives and lightly oil the blade. Linseed oil is a good lubricant and it works well for protecting wooden handles from dying and cracking as well. Store knives in their cases if you have them; if not ensure the blades are protected from possible damage and your knives are secured in a place out of reach of children.