1) learn HTML and make a simple website on a free host, next install there a free forum (like phpBB)
2) learn basics of PHP & MySQL
3) take a look on a free scrips source codes to understand how it works
4) make a design doc
5) write the game
6) find testers and put the game online, then fix the bugs
7) once everything is all right make a public release

administrate the game, make new releases, fix bugs, catch cheaters, organise promotion, find helpers
9) go to point 8 and repeat