PHP is the only one of those three you can learn quickly, and have to be interested and willing to learn, its not an easy thing to pick up.
PHP is a very simple server side programming language that mimics the code of C# or C++ I believe, and has the easiest methods of writing variables. I have been writting in PHP for 3 years now and the best way to go about it is to buy a web server with PHP and MySQL and learn to write some simple web applications. You can also install PHP on your own machine, but it's not a simple task for someone with little to no programming experience.
.NET I am taking up now in college. There is no way you can really learn this quickly, the best way to go about it is to take up classes or buy a book. Compare the ways of writing variables in PHP vs. .NET:
PHP
$variable = "Hello World!";
.NET
Dim Variable As String
Variable = "Hello World!"
It takes time to learn how to write variables that can be used in different functions effectively in .NET, as well as .NET has standards for creating variables to go by that take a long time to learn.
I know little Java, but Java is a very high end programming language and I say you are best off, also taking up some classes on it or buying some books.
Beings you are a first time programmer, I would strongly recommend learning PHP. I love PHP and it's very simple and powerful to write applications with. The others do have their major advantages over PHP such as having framework and the ability to run and write actual computer programs in, but they are much more difficult to learn and there are less resources available on the internet for them to learn off of, where as PHP has several tutorial and website to help you get started.
PHP also has the best documentation website, www.php.net, which features examples and input from other coders on actual functions and pieces of code in PHP.