Command Buttons display a standard command button (a rounded rectangle displaying text). When the user clicks the button it calls the associated function in Logic using the OnClicked event callback. They are not associated to any underlying parameters (see Changing the Layout).
You create them using the PPGLayout.AddButton or PPGLayout::AddButton method with the ScriptName argument and an optional Label argument:
# ** during control creation (for example, in the DefineLayout callback) **
oLayout.AddButton( "Reframe" );
//...
# ** as part of the logic attached to the custom property **
function Reframe_OnClicked()
{
// call other functions, get or set parameter info, or
// write any other handler code you want here.
}