This process is where unspecialized cells become specialized to perform specialized functions. This may occur through gene expression, where specific genes in the DNA are activated or deactivated. This is controlled by external signals. There are many differentiated cells in the body many such as muscle cells, blood cells, etc. These all preform special functions to keep the body running smoothly. All these specialized cells combined create a complex system, which also multicellular organisms to thrive. 

(National Cancer Institute, What is Cell Differentiation?, 2023)

This is controlled by gene expression. Only certain genes are activated in the cell, which leads to its unique structure and function. 

(Science Direct, Cell differentiation, 2021)