You've already used cPanel's AutoSSL tool to get your free certificate setup, and you've enabled the Force HTTPS option in the cPanel >> Domains page, but the browser still shows a warning when you access your site with an https connection.
This problem happens when portions of the page are using insecure links. You may see something like this in Firefox:
or something like this in Chrome:
To get the SSL working properly in the browser, you'll want to make sure all the links in the site's code also use https. Once that is resolved the SSL will no longer show that mixed content warning in the browser and your sites are fully secured.
If you are specifically seeing this problem with a form on your website, the following article may be helpful:
We have much more detail about what causes this issue and how you can resolve it at our Tutorial page here: How to fix mixed content warnings