I don’t understand the differences between each distribution. Is there a real difference?

The big one: a different combination of packages, i.e. which versions are available, and how they're configured and integrated. This generally also means they will have different package managers and configuration tools. Things have gotten a lot more regular between distros but there's still notable differences in philosophy between them, how much you notice kind of depends on how much of a power user you are and how prone to breakage your use-case and preferred applications are.

Distributions are like cars. They all get you from point A to point B, some of them will suit you less than others, and some people are really picky about which one they use for reasons.

Yes, depending on the distributions you are comparing the differences are trivial to radical to the point of making comparisons impossible.

> Is there a real difference?

The main differences are related to packages. The package format (.deb, .rpm, etc), the package manager (dpkg/apt, pacman, dnf, etc), how frequently the packages are updated, if they focus on stability or new features, etc.

New Linux users that are used to Windows or Mac sometimes dislike a distro and like other, but actually what they really disliked what the desktop environment. For example, Kubuntu uses KDE Plasma as its desktop environment and its user experience are almost the same as Fedora KDE, Manjaro KDE, OpenSuSE and so on, while it's very different to the default Ubuntu (that uses GNOME). But, under the hood, Ubuntu and Kubuntu are the same (you can even uninstall KDE and install GNOME).

Actually, other Unix-based systems can install the same desktop environments that we have on Linux, so, if you have a FreeBSD with KDE you won't even notice the difference to Kubuntu at first, even though it's a completely different operating system.

tl;dr: there's a real difference, but from a user perspective it's mostly under the hood, not exactly in usability.