How do cells. tissues, organs, and organ systems work together in a multicellular organism?

First of all, you need to know what cells are.

Cells are the organic building blocks for most organic matter. All cells have cytoplasm, a nucleus, mitochondria, a cell membrane and many other elements, depending on whether they are a plant or animal cell.

Cells live,move, and work together in order to perform a common function.
A Group of cells is called tissue.
Tissues work together by combining with other types of tissues in order to create an organ, such as your heart.
Different organs function and work together to make a organ system.

Hope this helps! :)