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To walk around you can press arrow keys or W,A,S,D. To jump just press space. You can also move around by simply left clicking at a location. Your avatar will move to that point.
To enter fly mode, press 'F'-your avatar will start to hover. To fly up, press 'R' or 'Page Up'; to descend, press 'C' or 'Page Down'. Use 'W' to move forward, 'A' to go left, 'S' to move back, and 'D' to go right. Press 'F' again to exit fly mode and land.