SSL Port, also known as Secure Socket Layer port is by default related to HTTPS, re web server and work on port 443.
SSL is a protocol that one can use to transfer data i secure tunnel and not as plain text, so it is not the ssl port that matter but what is the application that use it, when we use the normal HTML protocol to send and get data from the web everything that we send or receive is in plain text, this mean that it is possible to anyone to read the data, exactly like you are reading this article when we apply the ssl to the data on alternative port, re ssl port, the data become encrypted and it is much harder for user to read the data.
How SSL works:
When a web site is used SSL to encrypt its data the following is happens, the web site install a certificate to the site, this certification include a public key, a date that tell till when this certificate is valid and the authority that generated this certification , there are some types of certificates and there are some organisation that allow to sell certificate.
From now on the protocol is change to HTTPS, to notify that this is secure site, and all the data that transfer between the site to the user and from user to the site is encrypted, the user use the public key from the site to encrypt the data before sending it to the site, on the site there is a secret private key that known only by the site, with this key, and only with this key, the site is able to decrypt the data that was send from the user and to use it.
There are also some option to use the ssl certification you can buy one yourself or use a shared one from your hosting providers, starter site may use the share one, but compies will want to use their own certification for extra trust form its users.
SSl is the most whily secure method that used world wide, include credit card, banking and other sites and companies, there is an open SSL, free SSL integration open source that developer can use in their site creation and in any tool that thay want to develop, this way thay can use the ssl port tht thay want to the application they creating.