Look at the printed circuit board (PCB)
and be sure you understand how it should be oriented. Most of the components
will be placed on top of the board while
it is oriented as shown at left. This is the side of the board which
will face the outside of the box. The last two components you will
solder--the connectors to the stepper motor and the side power connectors--will
the opposite side.
Notice that the board is "double sided"
meaning that it has lines of metal printed on both top and bottom.
These metal traces are the "wires" which will conduct electricity.
The holes are "plated through" so
metal (and electricity) pass through the board at those points.
The board is also coated with a protective
covering, so the metal is only exposed in and around the holes. Some
of the larger holes have no metal traces, since they will be used
for mechanical connections, not electrical connections.