You can extend the existing modeling functionality of Simulink by creating new blocks and adding them to the Simulink library browser. Use a custom block to:
Model behaviors that are not provided with a Simulink built-in solution
Build more advanced models by using existing simulation
Encapsulate model components into a library block that you can copy into multiple models
Provide custom user interfaces or analysis routines
For information about creating a custom block based on your specific workflow, seeComparison of Custom Block Functionality.