Http send data in clear text format, hence middle man attacker or sniffer can read and understand data clearly.
Https sends data in encrypted format, which means clear text data is converted in “23423#$%#$2asd&*” encrypted format which only received can understand.
SSL protocol helps establishing the secure connection between client and server. Basically server send the ssl certificate to client, ( so before sending sensitive data client knows host server can be trusted and understand the in encryption details).
TLS 1.2 is successor of SSL which is current being used.