You having a certificate will not make your Moodle site secure.
There may be people out where who will, in exchange for money, offer to sell you a certificate that claims you know about Moodle security, but that is pretty meaningless.
Have you tried following the links at the top of this forum, and reading the advice there? That will increase your understanding of Moodle secuity. Also, Moodle is a fairly standard Web application. You mostly don't need to know anything special. You just need standard security practice for any server running PHP.
There may be people out where who will, in exchange for money, offer to sell you a certificate that claims you know about Moodle security, but that is pretty meaningless.
Have you tried following the links at the top of this forum, and reading the advice there? That will increase your understanding of Moodle secuity. Also, Moodle is a fairly standard Web application. You mostly don't need to know anything special. You just need standard security practice for any server running PHP.