The SSL certificate contains information about the certificate:
- Domain Name(s)
- Public Key
- Company
- Issue Date
- Expiry Date
- Issuer
And more

Client encrypts message with a public key supplied by the website that ONLY the server can decrypt!!
NOTE: This private key needs to be stored in a safe location on the server with the correct permissions and so it is NOT accessible by anyone outside the server

To prevent an attack on the certificate, this cert is cryptographically signed by someone else's private key so that the signature can be verified by anyone who has the corresponding public key.