Text editors

You need to find the init code first - if you are using Glen's TinyMCE integration check theme/tinymce_integration/footer.html

That example gives you source and from that example you can take the yellow parts

<script type="text/javascript">
tinyMCE.init({
mode : "textareas",
theme : "advanced",
theme_advanced_buttons1 : "mybutton,bold,italic,underline,separator,strikethrough,justifyleft,justifycenter,justifyright, justifyfull,bullist,numlist,undo,redo,link,unlink",
theme_advanced_buttons2 : "",
theme_advanced_buttons3 : "",
theme_advanced_toolbar_location : "top",
theme_advanced_toolbar_align : "left",
theme_advanced_statusbar_location : "bottom",
plugins : 'inlinepopups',
setup : function(ed) {
// Add a custom button
ed.addButton('mybutton', {
title : 'My button',
image : 'img/example.gif',
onclick : function() {
// Add you own code to execute something on click
ed.selection.setContent('<STRONG>Hello world!</STRONG>');
}
});
}
});
</script>

Note that the last row in init code does not have  ","  at the end - all other rows in init code have "," at the end.