In the same way that every telephone has a telephone number, every computer on the internet has an IP address.
In simple terms it is just a number. Quite a large number (there are roughly 4.3 billion IP addresses), but still just a number.
To make that number easier for us to remember it is broken down into segments, similar to how people tend to represent phone numbers in blocks of 3 or 4 digits. Which is easier to remember 3232235521 or 192.168.0.1?
Historically, those segments also had another meaning: they were used to divide up the IP address range into smaller pieces, each of which was managed by a different organisation, but nowadays the division is more granular and can’t be represented this way, so it’s just a display convention.
To be completely truthful here, there are two types of IP address: IPv4 and IPv6. IPv4 is the type I’ve described above – that’s the one most people use at the moment. IPv6 numbers are much bigger and represented in a different way. See What Is IPv6? for more information on that.