In R2019b and later releases, the function 'sscnewfile' can be used to create new '.ssc' files for custom Simscape components. See the following documentation for more information on 'sscnewfile':
In R2019a and earlier there are two possibilities:1. Copy an existing ssc-file and change the content of it, so you can easily customize an existing component.2. Create a new script in the MATLAB Editor, click "Save as", and manually change the file name to end with '.ssc'
If you need more information about Simscape Language, then please check the following documentation:
What Is the Simscape Language?
Simscape File Types and Structure
Creating Custom Components
