PuTTY for SSH: What is it and why do you need it?
Well, if you really want to know what PuTTY is, you can head over to the official PuTTY FAQ, but I'm guessing after you see that wall of text (no offense to the creator of the software) you would probably rather read a quick article about it.
What is PuTTY? Without getting too technical, PuTTY is an extremely useful tool for logging in and communicating with your Linux server by command line. If you're familiar with Unix or Linux bash commands already then PuTTY will come very naturally to you.
Why would I need PuTTY? For many years I created websites without ever knowing what PuTTY was or why it was so powerful. I would do everything with simple FTP programs like FileZilla. PuTTY can be an extremely powerful tool for moving files around quicker, compressing files, uncompressing files, changing ownership of files, or managing all facets of your web server. One of the nice things about having a shared hosting environment is that most of the time everything is already configured for you so there won't be much need to use PuTTY to help you configure your server unless you have a very specific need.
That being said, there have been times where there have been a scare with data or a site needed swapped to another server quickly and using PuTTY I was able to execute this process, oh I don't know, maybe 100x faster? You can quickly compress an entire directory, download it, dump a database, send the files to another server, uncompress the files, import the database, connect a few things, and have the website back online within minutes if you get good at it.
That's just one example of why it's useful. It's gives you full access to a computers operating system by command line. There are even tutorials out there that will help you access a GUI. For example, sometimes I install a VNC server that I can connect to and manipulate the operating system like I'm sitting directly at the computer. But, that's a topic for a whole different article.
The applications for PuTTY are vast, and it's hard to really express exactly why you need it until you find yourself in a scenario that you do. It's also only about 3mb and is free.