SSL (Secure Socket Layer) and TLS (Transport Layer Security) encrypt your data for secure communication over the internet. Without this layer of protection, your traffic would be sent in plaintext that anyone could see.
SSL was the original version of this protocol developed by Netscape in the mid-1990s (who remembers that early popular browser?). When the protocol was standardized in 1999, it was renamed TLS. There was little difference between SSL and TLS. Today these are often lumped together simply as SSL/TLS.
What Does SSL/TLS Do?
As explained in What is Encryption and What is End-to-End Encryption, encryption uses the science of cryptography to generate complex keys. The exchanging of keys within communication packets ensures only the intended sender and receiver can read the data sent.