When you send an Action() function to a platform, it evaluates an expression. For example, use Action messages when you want the launch window to appear. A user chooses columns in the launch window and the script continues running after the user runs the analysis.
dt = Open( "$SAMPLE_DATA/Big Class.jmp" );
dt << Distribution( Action( doit ) );
doit = Expr(
New Window( "Bivariate", Bivariate( Action( doit2 ) ) )
);
doit2 = Expr(
New Window( "Oneway", Oneway( Action( doit3 ) ) )
);
doit3 = Expr(
New Window( "Contingency", Contingency( Action( doit4 ) ) )
);
doit4 = Expr();