Once your files are encrypted, the hackers will display some sort of screen or web page explaining how to pay to unlock the files. Typically, ransomware has a one week deadline which, once passed, causes the ransom to increase. Most ransoms start in the $300-$500 area, and once the deadline has passed, it will likely increase to over $1000.
Paying the ransom invariably involves paying a form of e-currency (crypto-currency) like Bitcoin, also called BTC. Once the hackers verify payment, they provide decryptor software, and the computer starts the arduous process of decrypting all of the files.