Volleyball shoes (http://shop.volleyball.com/) provide the best support and grip possible for play. Running shoes work as well, make sure they are comfortable and you can jump in them.
Volleyball is stressful on the ankles. There are a variety of ankle braces available, the best being Active Ankles (http://www.activeankle.com/). Ankle braces are almost a necessity for anyone with previous ankle problems and a great preventative tool against injury. I highly recommend getting Active Ankles to anyone having concerns about ankle injury. Ankle injuries are the most common in volleyball and can be quite painful and take along time to fully recover from.
Kneepads are recommended but not required. Having that barrier and sense of security when diving sometimes makes players play harder. On the other hand it would be my hope that players player hard whether or not they are wearing kneepads. Kneepads come in all shapes colors and sizes, pick ones that are comfortable to you.
Players must wear athletic clothes to practice (shorts, t-shirt, sneakers) and be prepared to work indoors or outdoors. I encourage you to bring water or any sports drinks to practice or games.