Biology of Cells, Tissues, Organs, Organ Systems, and Organisms
A tissue is a family of cells that live very close together, and work hard to do the same jobs. Many tissues come together to form what biologists call an organ. This is like a city in the previous example. Organs then work together to form a system, and eventually the entire body of a lifeform.
In a way, your body is functioning as a mini-planet. Right now within your body, there are billions of individual cells working hard in specialized jobs. These cells join into tissues, organs and systems and help make up a vast community of life within you.