The first version of the IP protocol is now called IPv4 in order to differentiate it from the latest version of the IP protocol, which is called IPv6.
The main problem with IPv4 is that it is about to run out of IP addresses, which is the main reason for creating the IPv6 protocol. This happened because an IPv4 address is represented using 32 bits only, which allows a total number of 232 (4,294,967,296) different IP addresses. On the other hand, IPv6 uses 128 bits to define each one of its addresses.
The format of an IPv4 address is 10.20.32.245 (four parts separated by dots), while the format of an IPv6 address is 3fce:1706:4523:3:150:f8ff:fe21:56cf (eight parts separated by colons).
