They appear as blue square-shaped machines with an exit hole, sometimes leading to a pipe. The machine consists of many cogs and pipes which are constantly vibrating. Also, a blue arrow with red flashing lights and the word "START" on it in bright yellow letters appears on the machine.
Entry machines are at the beginning of each level and allow Norman Noggin to start the level. When Norman Noggin reaches the end of a level, jumping into the entry machine will let him progress to the next stage.