Adding a Format Style to the Drop Down list.

I am seeking to format paragraphs in the format of:
PARAGRAPH;
BLANK LINE;
PARAGRAPH;
NEW LINE;

I am not that handy with javascripts but I do know the structure of code and whatnot from my computer science classes I have taken. Does anyone know which file I need to edit? I can even just change one of the formats on there already if that is easier.

Thanks!