Here's a breakdown:

* Cells: The basic building blocks of all living organisms.

* Tissues: Groups of similar cells that work together to perform a specific function.

* Organs: Structures made up of different tissues that work together to perform a complex function.

* Organ Systems: Groups of organs that work together to carry out major bodily functions.

* Organism: A complete living being made up of organ systems.

So, for example, muscle cells join together to form muscle tissue, which then combines with other tissues to form organs like the heart or stomach.