Antivirus Prevents Malware?

Hi.. I am looking to find more information on this thing called ransomware or cryptolocker. I came across the term ransomware while I was viewing videos about malware on the Internet ( http://www.storagepipe.com/blog/DDoS-Bitcoin-Brute-Force-Malware/ ). Then the news of globally affected wannacry ransomware came out. I am trying to find more about cryptoware.
So, this cryptolocker encrypts user files in the background and demands money from user to decrypt them? How can we identify and block them? Even if our files are encrypted, isn’t there absolutely no way for us to decrypt and use it? Can Antivirus software like Kaspersky Total Security or Premium identify and prevent them being installed in the system?