Asociar Clases y Crear HTML

<button id="boton1">Asociar Clase</button>
<button id="boton2">Quitar Clase</button>

<p>Lorem ipsum dolor sit amet consectetur adipisicing elit. At ea nemo adipisci voluptates eveniet sequi quibusdam dolor rerum odit saepe non praesentium ab, fuga quidem laborum voluptatibus ad repellendus et!</p>

<!-- Scripts -->
<script src="js/asociarClases.js"></script>

.parrafo{
  color: white;
  font-size: 20px;
  background: green;
  padding: 20px;
  text-align: right;
}

$('#boton1').click(function() {
    $('p').addClass('parrafo');
});

$('#boton2').click(function() {
    $('p').removeClass('parrafo');
});

<button id="boton3">Agregar Caja HTML</button>
<div id="contenedor">
	<div id="c1">Hola</div> 
</div>

<!-- Scripts -->
<script src="js/crearHTML.js"></script>

$("#boton3").click(function() {
    // Reemplazar contenido html
    $('#contenedor').html('<div id="c1">Adios</div> ');
});