An SSL certificate protect the site navigation.
The URL of a site or a secure page starts with HTTPS://, where the "s" means secured. An example is https://misterdomain.eu
When do you need a SSL certificate:
- Will your site be any kind of e-commerce?
- Will your site need any login or do the user need to insert any kind of data and you need to protect it?
Advantages on Google:
Google helps the certificated sites, the https is a ranking factor that helps Google positioning.