The page you need is
http://calculo.mt.gob.do/ . You just enter the person's salary, this must include bonuses and any extra money you paid like a meal allowance or transport. You then enter the start and leave dates and it will give you the liquidacion to pay.
Remember, if you have fired them on the spot you need to give them the money that says "Preaviso". But if you have given them notice, ie told them a month before they are going to lose their job, then they don't get this.
The Cesantia is the amount to compensate them for losing their job. There is an option to say whether they had taken their holidays (as paid time off) or not, if not then you have to give them the money for holidays. And the Salario Navideña will be 5/12 of their extra Christmas wage (as we are in month 5).
Very important notes.
1) Most Dominicans, even the most illiterate, will have already worked out their liquidation. I usually start by asking them if they have done their calculations. Much easier to double-check theirs. If they want to go to the office of the secretaria, they can do and get their calculations done there, but basically it's exactly the same process as if you do it online. Make sure that you both agree exactly the amount of money they should be paid. There will always be an auntie / uncle / cousin / neighbor who is a lawyer and who is ready to take you to court (for a slug of the liquidation) so it's very important to make sure the person is genuinely happy with the calculations before you pay.
2) Before paying a peso, in addition to agreeing the calculations, you need them to sign a Descargo Laboral. This is a legal document which basically confirms they are completely happy with the amount and it wipes out any claims they have. Once they have signed this, they cannot then go to court. Always get them to sign before paying anything. (The document actually says that they confirm they have received the money, but I've never had a case where someone refuses to sign. Most of the time they are desperate for their money and I refuse to pay anything until I have the descargo in my hand). There are plenty of models of this document online, but if you are stuck I can send you one, just PM me.
I'm good at firing people!!!!