Knitting needles are available in a variety of types - circular, double pointed (DPNs) and straight. Your choice of needle will depend on what you like knitting with and what project you are working on.
Circular needles are used when knitting in the round or 'magic loop' - they are perfect for socks, gloves, hats and jumpers. DPNs are used when knitting in the round - they are pefect for socks, gloves and sleeves. Straight needles are generally used for flat knitting (knitting on the right side, and then turning and knitting on the wrong).