WordPress, like many other popular blogging softwares, is written in PHP. Sometimes people looking to start a blog, or a website of any kind, are worried about learning programming languages. But fear not, you don't really need to know how the software works to utilize it!
Installing PHP requires that you know some basic information about your hosting. And yes, your host needs to support PHP, but you'd be hard pressed to find one that doesn't.

Most of the information you need is simple to look up, or ask your host for. Once installed, you need no programming skills at all to run WordPress, make posts, change themes, etc. etc.

PHP is handy if you want to really dig in and customize WordPress. Most things you can find mods online for (that someone else has already written), but if you have very specific needs then it helps to know your way around PHP.