Don't feel bad, it is quite confusing.
SSL (Secure Socket Layer) is old, and pretty much dead. This is a old method of securing web content. Why do we still see people talking about using SSL? Keep reading. You cannot be PCI DSS (Payment Card Industry Data Security Standard) compliant (processing credit card data on your website) if you still use SSL.
TLS (Transport Layer Security) is the newer version on web encryption and what replaced SSL. It is much more secure then TLS when using the later versions. Companies/Websites that accept credit cards have until 2018 to disable TLS v1.0 in order to maintain PCI DSS compliance. TLS v1.1 & TLS v1.2 are the currently accepted versions to use.
HTTPS means your website is encrypted, using TLS.
So, if SSL is outdated, why do we still hear people talk about it and companies selling it?
SSL and TLS are often used interchangeably. If you need to secure your website using TLS, you purchase a SSL certificate. Which versions and which encryption your server uses to encrypt the data, depends on your server side settings.
A SSL certificate will secure your website using TLS, without using SSL at all.