There are two ways to overcome this problem. One is to use a kind of electric current that periodically reverses direction, which is known as an alternating current (AC). In the kind of small, battery-powered motors we use around the home, a better solution is to add a component called a commutator to the ends of the coil. (Do not worry about the meaningless technical name: this slightly old-fashioned word "commutation" is a bit like the word "commute". It simply means to change back and forth in the same way that commute means to travel back and forth.) In its simplest form, the commutator is a metal ring divided into two separate halves and its job is to reverse the electric current in the coil each time the coil rotates through half a turn. One end of the coil is attached to each half of the commutator. The electric current from the battery connects to the motor electric terminals. These feed electric power into the commutator through a pair of loose connectors called brushes, made either from pieces of graphite (soft carbon similar to pencil "lead") or thin lengths of springy metal, which (as the name suggests) "brush" against the commutator. With the commutator in place, when electricity flows through the circuit, the coil will rotate continually in the same direction.
For some kinds of motors, principally motors with terminal-based connections, basic wiring is self evident. The terminal board itself usually has markings that indicate where line one and line two are to be connected. But what if you need to reverse that motor, use a different (but available) voltage setting, or have a motor that has nothing more than a bunch of color-coded or numbered leads coming out of it?