Here's a breakdown of how it works:

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

* Tissue: A group of similar cells that work together to perform a specific function.

* Organ: A structure made of different tissues that work together to perform a more complex function.

* Organ System: A group of organs that work together to carry out major bodily functions.

Think of it like this:

* Bricks: Individual cells

* Wall: Tissue

* House: Organ

* City: Organ System

The process of making tissues is called "differentiation":

1. Stem cells: These are specialized cells that can develop into many different cell types.

2. Cell Division: Stem cells divide and create new cells.

3. Differentiation: New cells receive signals that tell them to develop into a specific cell type. This might be a muscle cell, a nerve cell, a skin cell, etc.

4. Tissue Formation: Once the cells have differentiated, they stick together and work together to form a tissue.

So, tissues are basically groups of cells that have been programmed to work together to do a particular job in the body!