show pagination for query

Hi, i have a query that i want to show pagination for, here is the code:

{% set args = {post_type: 'folders', posts_per_page: '6', nopaging: false, category_name: 'en-cours' }%}
{% set myfolders = mb.get_posts( args ) %}

{% for folders in myfolders %}

content is here

{% endfor %}

<div class="nav-previous alignleft">{{ mb.previous_posts_link( 'Older posts' ) }}</div>
<div class="nav-next alignright">{{ mb.next_posts_link( 'Newer posts' ) }}</div>

i added these two lines without success ! nothing displayed, any idea how to achieve this ?
if you can also tell me how to get page numbers to put between those two buttons

thanks