Arrow keys to move and Z to jump +/- to zoom in/out, IJKL to move the camera.
Hit the P key to toggle the ability to place blocks.
Hit backspace to delete the last block you placed.
Use the 0 or 1 keys to set the type of block.
Hit Q to toggle gravity.
While the gravity is off use 'V' and 'B' to adjust Y velocity.
Go here for the source code