I follow the lamp stack of Linux, Apache, MySQL and PHP I do this mainly because of cost, resources, a friendly and knowledged community can be easily found to help guide you on your way. This stack is also very wide used and for good reasons. So to your questions 1) What technologies should I start. PHP, MySQL, HTML, CSS, JavaScript (and the jQuery library). For local dev I use the abyss x1 http because its free and very easy to setup. If you work on a linux box getting mysql, php and apache is often bundled in a group of packages that is an easier install. But Apache has a lot more bells and whistles to make it more custom, which why I use abyss. The order I would train in is html and css, then javascript and jQuery, and then PHP and MySQL. Once you get to PHP/MySQL you will want to focus on issues of sessions and security. 2) How these networking sites are built, with user login etc. This is a big question but the short answer is sessions. Sessions store values placed in them by the scripts you write, like a posted form sends username and password to a server. a script on the server scrubs the input, to protect from hackers, and validates the info. If its correct then a session variable(s) is(are) set so you can maintain persistant data between page request. Session related variables can include user name, security level, a saved shopping cart, etc. 3) Is there any helping documents which I can refer to. To numerous to count. This site, "Code Project" is a truly great resource for code snips and guidance. And I do not get paid to write this...well I do not think I do...maybe I should ask ;) also: http://www.php.net/ , http://www.mysql.com/ , http://www.w3schools.com/html/ , http://www.w3schools.com/js/ , http://jquery.com/ , and a place to see where online applications are going sites like this http://html5demos.com/ give you a glimps of whats possible 4) What database technologies that I should learn. MySQL is the most common db engine you will find on the net.
Chris J www.redash.org