IPv4 is the original addressing system the internet was built on. IPv6 is its successor, designed once it became clear IPv4 didn't have enough addresses for a planet full of connected devices.
IPv4: four numbers, one big limit
An IPv4 address looks like 203.0.113.42 — four 8-bit numbers (0–255) separated by dots, giving about 4.3 billion possible addresses. That sounded limitless in the 1980s. It isn't anymore: phones, laptops, TVs, thermostats, and doorbells all need one, and the free pool of IPv4 addresses has been effectively exhausted for years.
IPv6: vastly more room
An IPv6 address looks like 2001:db8:85a3::8a2e:370:7334 — eight groups of hexadecimal digits, giving roughly 340 undecillion addresses. That's enough to assign a unique address to every grain of sand on Earth many times over, which was the point: stop running out.
Why you often see both
Most networks today run in dual-stack mode, meaning your device holds both an IPv4 and an IPv6 address at once and uses whichever the destination server supports. That's why the home page here shows a pair — your connection genuinely has both.
Does it matter which one I use?
For everyday browsing, no — both get you to the same place. IPv6 avoids the workarounds (like carrier-grade NAT) that IPv4 scarcity has forced ISPs into, which can make certain things — like receiving inbound connections — more straightforward on IPv6.