I recommend learning to program, by practicing, first. Preferably in a "better" language than PHP. By better, I mean a language that encourages better coding style.
My personal bias is to favor C# or maybe Python, but this is very subjective.
Once you've got some experience programming in general, writing a web application should be easier because you'll be able to learn the web specific stuff distinct from basic programming.
For a first web app, the easiest environment to start with and get something functional is probably PHP. That doesn't mean it's the easiest language to build a serious web app in. I don't like PHP as a language, but I did write my first web app in it. I now use C# (ASP.NET) for web programming and like it better, but I don't think this would have been an easy environment to start with. Still, you could start with anything and succeed.
Don't expect your first web application to be amazing! You'll be learning how http works, how to deal with statelessness, and much more as you go. Your first web code will probably be disgusting to you later on, but that's OK. Learn from it, and do better next time.
(This is all assuming you are actually serious about programming, because you aren't going to program a web app without programming. An alternative is to pay someone else.)