Anyone with the expertise and necessary tools can actually take a peek on the information you share online, whether you want to keep it confidential or not. Using SSH, one can set up a secured channel for information to safely pass from an SSH client to an SSH server and vice versa. This channel is protected from any unauthorized access from outside usually intended to intercept sensitive information for illicit use.
SSH uses what is called public-key cryptography in order to verify and authenticate a computer which intends to get access to an SSH-protected site. This is done by producing matching pairs of keys, one is called the public key and the other is the private key.
The public key is found on computers from which access to information is desired, while the private key is kept by the owner who is allowed said access. SSH will then verify whether the one offering a public key is also the same person who owns the corresponding private key. This process is often called associating public keys with identities.
Now that you know what SSH means, you may wonder whether your site needs it or not. And if the answer is yes, your next question is where and how you can get it. First of all, SSH is not a prerequisite for any website. You can create and run a website without even knowing what SSH is and that it even existed. SSH is installed and used on websites for only two reasons. First is to allow the user to directly access the web server, and second is for protection of sensitive information received on the website.
SSH finds significance in a web hosting environment. Basically, websites are hosted by web hosting providers through their web servers. These web servers control pretty much everything on the hosted websites, from storage and bandwidth to scripts and web contents. Web servers have direct access to your websites, but not the other way around.
SSH is the exception. Some web hosts allow direct access to their servers via SSH channels. This is significant for some web masters who wish to manually make some alterations on the web server and are authorized to do so. Some command lines need to be remotely executed on the server. This is possible with a web host having SSH support.
As mentioned earlier, online security is another reason why SSH is installed. Using SSH, you can establish safe channels to accept sensitive information from your site visitors without fear of losing them to packet sniffers or hackers. The SSH keys will ensure that only those with authorized access can see and use the information passed through the network.