What does the following command do in PHP?
. $string // ($string is something which i declared in the program)
Your statement would throw back an error.
The "dot" is a string concatenator. That is, it helps you to combine strings together into another string.
Example. $full = $part1 . $part2;
Concerning getting started: That's a difficult question. PHP.NET will be your functional looking site. Google-ing just about anything on PHP will direct you there. I'd look at getting a localhost setup of PHP/MySQL/Apache. If you're on a Windows machine, you can get a WAMP server setup.
http://www.wampserver.com/en/
This will drastically speed up your development and testing time. Don't try to FTP everything up to a Web server, as this approach will waste away 10-15% of your working time. Work smart - work local.
Find an existing project (Open Source) with a great community and just try to start something. For example, I recently created DogFriendlyOlrando.com based on WordPress. I was curious as to the abilities of WordPress. It was a fun little project and gave me a good understanding of WordPress' capabilities. You'll learn the most from just diving in and doing. Good luck!