can someone help explain how Serotonin works?

Serotonin is a neurotransmitter created by the nervous system. A neurotransmitter is a chemical substance released by a nerve cell that transmits an impulse to another nerve, muscle, organ, or other tissue. How the nerve cells communicate is rather simple: (1) the first nerve cells puts the neurotransmitter between it and another, a place called the "synapse" or "synaptic cleft", (2) that other nerve cell has receptors that recognize that neurotransmitter, (3) the second nerve cell that received the neurotransmitter creates a response. Serotonin's creation specifically are usually stopped by its being taken back into the neuron then releasing it for it to be recycled for reuse or broken down and transported out.

As for how it affects people, serotonin has been called the "happy neurotransmitter". It helps with feelings of relaxation and happiness. Deficiencies of it is where we believe depression, anxiety, insomnia, and other various problems come from.