To play this game i just need to buy it somewhere??
Do i need to pay every month to play it??
Can i run FF XIV on this PC:
Pentium Dual Core E5700 3.00 Ghz
4 GB Ram
Nvidia GeForce 230 GT
Yes, you have to buy the game to play. Most retailers have it for $20 or so these days.
Yes, they are currently charging for subscriptions as of the beginning of this year. The monthly rate for one character is $10/month, lower if you commit to three or six months at a time.
Your specs are a little low for the game, however. Sometime next year they will be "relaunching" FFXIV in what's known as "version 2.0." It will be released for both the PC and PS3 and it's expected to have less stringent minimum requirements to play. It may be worth the wait.