How can I install apps/modules in odoo v9
<p>I have started using <strong>odoo</strong> and I would like to install some <strong>modules</strong> like <strong><a href="https://apps.openerp.com/apps/modules/master/report_custom_invoice/" rel="nofollow">Custom Invoice template</a></strong>, Pls recommend some docs or steps to install new modules.</p>