There is a direction to the flow of electricity. You have to keep track of the direction of the electrical current in order to understand a circuit. Some devices will not work properly if the current is flowing the wrong way.

Here are some examples:

A D-cell battery has two ends. By convention, the direction of flow is from the positive end (the top of the battery -- the end with the bump on it) to the negative end (the bottom).

Many electrical components, like the motor in your kit, have wires that are different colors. The red one is to be connected to the positive end of the battery, and the other (whether blue or black or almost any other color) is to be connected to the negative end. If you connect it the wrong way, it may do the something different, or even not work at all. There is a current flowing, and that it has to go in the right direction. The current goes in the red wire, and comes out on the black wire.

Attach a piece of tape to the shaft of the motor, to make a little flag. Then observe what happens when you reverse the direction of the current in the motor.

Does a light bulb care which way the current is flowing?

What does the little box with red and black wires do?