- create new MPS project containing your language definition (SimplestLanguage) and 'sandbox' solution which uses the SimplestLanguage;
- create definition of the SimplestLanguage. I.e. its structure (abstract syntax), editor (concrete syntax) and generator (semantic);
- create test model, write some 'code' using the SimplestLanguage and generate the solution to text (shown in the output view). You can also choose to generate java files from the solution.