Transport Layer Security (TLS) and its predecessor, Secure Sockets Layer (SSL), both frequently referred to as "SSL", are cryptographic protocols that provide communications security over a computer network.
The server checks what the highest SSL/TLS version is that is supported by them both, picks a ciphersuite from one of the client's options (if it supports one), and optionally picks a compression method. After this the basic setup is done, the server sends its certificate.
SSL stands for Secure Sockets Layer and was originally created by Netscape. SSLv2 and SSLv3 are the 2 versions of this protocol (SSLv1 was never publicly released). After SSLv3, SSL was renamed to TLS.