Adding to the above, you may not have realised, but this is a subscription based MMO. You need to pay a monthly fee if you want to play.

Entry level is £7.69/€10.99/$12.99 a month
Standard is £8.99/€12.99/$14.99 a month (although gets cheaper if you buy more months at a time and 6 months at a time is the same price as entry level)

Entry level only allows one character per world which is probably all you need. Standard allows 8 per world.

Alternatively there are timecards you can buy other places which are always "Standard" level, although these are rarely cheaper than just subscribing directly with Square Enix.

Hope this is of some help!