The "suit" is an 8 foot tall machine that is worn by an actor and controlled partially through body movement and partially through remote control.
The actor inside is standing on several inches of lift boots but his legs do extend through most of the suits legs. The outer portion around the hips and the hinge joints is wider than the actor and serves to make it appear robotic. But the legs are completely human powered which is why it is capable of such precision and fluid movement.
The actors upper body, including head and arms are inside of the suits "chest" area. There is a visible mirror on the front of the chest which is where the actor can see out, much like the mirrored visor on a helmet.
The suits shoulders, arms and head are above the actors real head (and reach a height of 8 feet). This upper portion of the suit is a remote controlled machine. The actor inside has a control panel inside the chest which allows him to pilot the upper portion of the suit. Most of the actions and sounds are prerecorded gestures which are simply triggered in sequence by selecting the proper commands.
The actor also has a voice modulator which allows him to speak during performances.
In addition the remote controls can also be taken over by his assistants which are watching from a distance in case of any danger or threat that needs response which the actor can not see (for example if a child wanders in range of a movement from the suit which the actor cannot see to his side or behind him, the assistants can override his movement and try to prevent harm to the child).
During performances there is also usually in-character security (men in black suits) that are used not only to add to the mystery of the presentation but to keep people from tampering with the panels and latches that keep the suit from opening up and revealing the person inside.