What order should the Fairy Tail volumes/chapters be read in? And how to read labelling "Fairy Tail 465 - 400 Years"?
You should read the chapters in order from Chapter 1 to the latest. On the majority of the websites they will put the latest characters (based on chapter number) towards the top of the page.

As for your second question: Fairy Tail 465 - 400 Years; means the that is chapter 465 of the series, and the title of that particular chapter is '400 years'.

As an FYI to you, there are several other Fairy Tail series that are pseudo-canon (or fully canon) related to the main story. Some of them are written by the same author of the core series. Just be warned that some of them have spoilers for historic events of the main series, but they are all really good.