All socks perform the same basic functions. The difference is that high quality socks perform those functions better than their cheaper counterparts. Socks protect your foot from your boots. They cut down on friction, which reduces your risk of blisters, scraps and chafing. It is also suppose to keep your feet comfortable.
Often, a quality sock will consist of several different types of fabric. Generally, strong fibers will be used to reinforce the toe and heel. Stretchable fabrics are used at the top of the sock, where they hold the sock securely to the calf. Acrylic fibers are used to keep the sock dry, and heavy knits help prevent blisters.