Electricity can be painful or even fatal to our bodies in large doses, like a bolt of lightning, or the electrical chairs used in some states to execute criminals. But the body uses electricity in much smaller doses all the time. In fact, electrical signals are a key component in the communication system between the brain and the rest of the body.
The brain contains roughly 100 billion nerve cells, called neurons. It's their job to gather and transmit signals, similar to the way the gates and wires in a computer operate. There are many different types; the shape of a neuron gives it its function. Muscle contractions are controlled by motor neurons, which carry signals from the central nervous system to the muscles, skins and glands in the body. Those signals are transmitted over neural pathways.
The simplest type of neural pathway is a reflex pathway -- for example, the knee-jerk reflex you experience when the doctor taps just the right spot on your knee with a rubber hammer during an examination. A sensory neuron detects the tap and passes an electrical "message" to a motor neuron, telling it to release a neutrotransmitter (a communication chemical) to the muscle cells, causing them to contract or expand in response. The reaction is so simple, the brain isn't needed. But for more complex tasks or functions, much more complicated "circuitry" is required.