I'm making my university community web service with a team. (6 members myself included)

And we decided to use JavaScript, HTML, CSS (for sure, it's the basic of websites) but couldn't decide for the back end part.

There are tons of languages, tools, etc., but I'm really new to programming, so I'd like to get some help to figure out what tools we need.

So my question is this: are there any good examples of web community services we can mimic the tools or get an insight from them?