When a group of cells that all have the same basic structure and function come together, they form a(n)

When a group of cells that all have the same basic structure and function come together, they form a tissue.

These cells are usually specialized cells that have specific functions that would make the tissue functions as it is. These specialized tissues gather then form what you call an organ. Then these organs come together and form a system. Systems then come together and form an organism. These tissues that come together make up a unique organ and so on and so forth.