I've poked around in various languages while deciding which I would 'get good' at...now I'm no expert on the languages I'll toss out here but long ago I came to (
vaguely) understand their rolls in getting a site up, running and functional.
HTML: This is the code to get the site running, bare bones web code basically. It's absolutely necessary and you will be using it even if you don't realize it or not (say you use a 'template' service to skip lower level code...well they will be using HTML) It comes in various iterations -HTML4 -HTML5 -etc'
CSS: Short for "Cascading Style Sheets" this language will make your functional HTML site beautiful and ascetically pleasing. Odds are it does quite a bit more than that but that's my understanding of it in a nutshell.
C#, Javascript, various similar languages: These languages will do a
LOT for your site. This is where you will cook up the various "functions" for your website, that C++ project you made...imagine putting it on a website for people to access on a webpage. These languages can do other important aspects you would need for your proposed site, some are great "go-between" languages for server functions, and getting certain lower-level languages to "play nice" with each other...
PHP and other server specific languages: Someone bids on an item and wins, that data has to be stored on a server, someone's gonna have to get that aspect up and running. I know of at least two "server" languages but only PHP is coming to mind at the moment and odds are there are more.
There's quite a bit of cross-functionality in that some languages can do the jobs of others. For instance I know you could use C#'s 'ports' to cover quite a bit of the server functions and with a bit of creativity you could use it for a bit of "prettyfying" and thus intrude into PHP's area.
And that's about my knowledge on the subject, odds are there's better methods, languages and such, also my knowledge is pretty dated lol...I honestly don't know wtf Python or Ruby does but I bet there's a good reason so many use them.
You're gonna want more input than mine basically.
Good luck with the site sir.
Edit- The people here are mostly game devs btw, cool people and I bet quite a bit here have web development skills but you are likely to get the best answers
>Here<...Stackoverflow if basically the internet Olympus of coders and they will stumble over each other to accurately answer/help you learn/debate each other openly about the best methods/ etc...great people there as well.