This controls what buttons you want show up in the toolbar.

Space separated list of toolbar controls

tinymce.init({
toolbar: "undo redo | styleselect | bold italic | link image"
});

Disable the toolbar

tinymce.init({
toolbar: false
});

Multiple toolbar rows

tinymce.init({
toolbar: [
"undo redo | styleselect | bold italic | link image",
"alignleft aligncenter alignright"
]
});

You can find a complete list of buttons here.