I'm not going to explain HTTPS to you here but I'll leave it to Robert Heaton in this comprehensive article.

Soon Google will not index your site unless it issecured with SSL (HTTPS) so you might wnat to ask your hosting provider what options they have for securing it. Here at clickmarlow.co.uk we have a blanket certificate which verifies the domain and allows you to have the "Secure" padlock in the address bar. Remeber too that the whole of your site has to be secure. You can't pull scripts from CDN servers which have not been secured as you browser will tell you that unverified scripts are trying to be loaded. Google Chrome allows to go ahead and load them by clicking the small red icon in the address bar ... for now ... I think this will change shortly.