You use input devices to communicate your intentions and actions to the virtual world. Since it is often difficult to touch-type or use a mouse while standing up and wearing a head-mounted display, other types of input systems are used instead of or in addition to keyboards and mice.
A wand is basically a hand-held joystick with a number of buttons on it. Wands often include a tracker which then allows you to pick up and rotate objects in the virtual world. You can use a wand in VR in much the same way you use a mouse on a computer desktop. Moving the wand in space moves a 3D pointer in the virtual environment. You can also click and drag virtual objects, but instead of just moving them vertically and horizontally, you can also move them in depth and rotate them about all three axes. This is why wands which can move objects in the X, Y, and Z directions and also rotate them about the X, Y, and Z axes are sometimes called six-dimensional or 6D controllers.
Since distances can be arbitrarily large in a virtual environment (and trackers have a limited range) it is not usually practical to travel through VR on foot. Some of the wand buttons are often used for "flying": you pointing your wand or your head in the direction you wish to travel, and then press the "fly" button. In VR, there is no speed limit.
VR gloves are like wands, only more complex. They consist of a tracker to sense the position and orientation of your hand, and some kind of flex sensors to measure the bend of your fingers. Gloves tend to be expensive and tricky to use partially because the computer must be able to recognize intricate hand signals instead of simple button presses.
Body suits are also used to sense the users body positions and also to provide some tactile feedback to the user.