What are the major differences between Node.js, PHP and Golang?

I'm trying to determine which back-end language I should learn first. But I'm somewhat confused as to how they differ.

What I've read so far is that Golang focuses on concurrency and large scalable applications.

PHP has been around for a long time and most CMSs are based on it.

Node.js is relatively new and light-weight JavaScript-based alternative.

But I'm not sure how much of this is true and which language is right for a new aspiring web developer.