SSL error - do I need to add rewriting rules in order to get rid of unsecure error messages?

[Lory]

Hello,
I have install a ssl certificate on my server and then i enabled ssl from prestashop back office but i am getting unsecure errors and this certificate can not be trusted errors.
I talked with the hosting company and they told me I need to add redirects from http to https for the check-out process.
Did anybody do this? Can you guys please help me with this?

Thank you,
Lory