Short answer
IPv4 and IPv6 are two versions of the IP protocol. They run side by side because the internet is still moving from IPv4 to IPv6.
Address format
IPv4 uses four numbers, for example 192.0.2.10. IPv6 uses hexadecimal groups, for example 2001:db8::10. IPv6 addresses are longer because the address space is much larger.
Why IPv6 is needed
IPv4 has about 4.3 billion addresses. That is not enough for today’s internet with phones, servers, cloud services and connected devices. IPv6 solves the address shortage.
Why IPv4 still exists
Many networks, systems and services are still built for IPv4. That is why many connections use dual stack, where IPv4 and IPv6 both work at the same time.
Common questions
Is IPv6 more secure than IPv4?
Not automatically. Security depends on firewalls, configuration and updates.
Do I need IPv6?
You do not need to do anything if your provider handles it, but IPv6 is increasingly important for a modern internet.