What is the address classes in IPv4?

There are three "classes" of IPv4 subnets. Essentially, these refer to which "octet" is set.

Class A: A /8 network (netmask 255.0.0.0) - the first octet is set and the rest belong to you. i.e. 128.x.y.z. You have 256x256x256/2^24 IPs available here.

Class B: a /16 network (netmask 255.255.0.0) - the first two octets are set and the rest belong to you, i.e. 128.67.y.z. You have 256x256/2^16 IPs available.

Class C: a /24 network (netmask 255.255.255.0) - the first three octets are set and the use of the fourth is yours, i.e. 128.67.4.z. You have 256/2^8 IPs available.

It's possible your question may have meant types of addresses used (for routing purposes). There are broadcast addresses (send a packet to everyone on my local network), unicast (basically point-to-point connections, the most common) and multicast (senders/receivers communicate through a multicast IP, sending one packet to many destinations with just one transmission).