If you receive a "website is insecure" type message or the browser padlock is missing after installing an SSL certificate then please see below.
This can occur when you have mixed content of HTTP and HTTPS referenced items.
Mixed content occurs when a webpage containing a combination of both secure (HTTPS) and non-secure (HTTP) content is delivered over SSL to the browser.
To fix this you would need to be able to identify the non secure content within the code of the site and ensure all referenced items are being called over HTTPS.
Most common day browsers like Google Chrome and Mozilla Firefox have an ability to look at the code in a developer stance meaning its like a debugger console built into the browser.
In Google Chrome you would right click on the page that is displaying the warning and select "Inspect."
On Mozilla Firefox same idea but they call it "Inspect Element."
Look for any "Mixed Content" warnings or items being referenced with plain HTTP and not HTTPS.
You can then edit the code in your pages to ensure those items are changed to call via HTTPS.
If you are using Wordpress also make sure that you install a "Force SSL" plugin to automatically make all pages SSL secured.
An in depth guide to this subject is given over at Google's developers guides: