IP addresses
For a message to reach the right computer, that computer needs an address — a unique label the network can deliver to. That's an IP address (IP = Internet Protocol). It's the 'house number' of the internet: write it on a packet and the network knows where to send it. Without addresses, a message would have nowhere to go.
An IP address is a unique number for one machine
You've probably seen one: something like 142.250.72.14. Those four numbers are just a way of writing one big number that's unique on the network — no two machines you're talking to share it at the same time. When your phone sends a request, it stamps the packet with two addresses: the destination (where it's going) and its own (so the answer knows where to come back). The network reads the destination and hands the packet along, router to router, until it reaches the machine with that number. Exactly like mail: the address on the envelope is how it finds the house.
IPv4 and IPv6 — we ran out of numbers
The old style (IPv4, like 142.250.72.14) has about 4 billion possible addresses. That sounded like plenty in the 1980s — but with phones, laptops, TVs, and smart fridges, we ran out. So there's a newer, much bigger style called IPv6 (a longer address like 2001:0db8:85a3::8a2e:0370:7334) with so many addresses we'll essentially never run out. You don't need the details — just the idea: addresses are a limited resource, and we had to invent a bigger pool.
Public vs private: your address at home is shared
Here's a twist. Inside your home, each device gets a private address (like 192.168.x.x) that only means something on your local network. But to the outside internet, your whole house usually shows up as ONE public address — your router's. Your router does the translating: it remembers which inside device asked for what, so when answers come back to the single public address, it forwards each to the right device. That trick is called NAT, and it's a big reason we didn't run out of IPv4 addresses even faster. (We'll cover NAT in its own topic.)
Questions you might have
▸Is my IP address like my home address — does it reveal where I live?
Roughly which city or region, not your actual street. An IP can be traced to a general area and your internet provider, but it's not a precise GPS pin. It identifies a network location, not a person standing somewhere.
▸Does my IP address ever change?
Often, yes. Many providers give your home a public address that can change over time, and your private address (inside your home) can change when you reconnect. Servers usually keep a fixed address so they're always findable — that stability is part of being a server.
▸If addresses are just numbers, how do I get a name like google.com?
Names are friendlier than numbers, so there's a phonebook that turns a name into its IP address — it's called DNS, and it's one of the most important systems on the internet. We give it a whole topic of its own.
▸Can two computers have the same IP address?
Not at the same time on the same network — that would be like two houses with the same address; deliveries wouldn't know where to go. Private addresses CAN repeat across different home networks (your 192.168.0.5 and your neighbor's are separate islands), but public addresses on the open internet are unique.
Best read after: What is a network?