At the end of the day, all Linux distributions are pretty much the same. At their core, they are all still the same operating system running the same software.
The biggest differences between the distros are their package management systems and tools.
Debian (and derived distros) use the Debian (.deb) package format, Red-hat (and derived distros) use the RPM (.rpm) package format. And distros like Arch and Slackware use their own packaging formats and tools.
Packaging differences aside, some distros - like Debian Testing, Fedora (Red-hat based) and Arch tend to use newer versions of the Linux kernel and other software packages. But this comes at the cost of potential instability and breakage - which can happen from time to time after updates on these systems - albeit rarely.
Whereas distros like Debian Stable and RHEL use older, better tested versions of software. Although they use slightly dated, older software - they are considered to be much more stable. Also the package maintainers always keep the software patched with the latest security updates.
The only other differences are the desktop environments and the set of software that they ship in their default install.
Most distros offer a full desktop environment with a set of pre-selected programs (media players, browsers, editors etc) - distros like Debian, *buntu, Mint, Fedora, Suse etc....
Most of these distros aim to give a quick and convenient way to get Linux up and running on your machine. But the cost for this convenience is that you might have a little extra bloat (additional drivers/services installed that you don't actually need). A small price to pay!
With other distros like Arch and Slackware, you start with the bare minimum required to be able to boot into a Linux terminal and you build/customize your system from there by adding whatever software you need. This way you can tailor your operating system to your machine without having lots of unnecessary packages installed. So you can expect blazingly fast boot times and great performance. But the cost here is the time and effort required to install and configure everything.
There are other minor things that differ between different distros, but above are the only real big differences.
There are also some distros that target different types of users - like Ubuntu Studio, which is aimed at content creators - people who make music, videos and art and is loaded with all of the tools and programs artists/videographers and musicians will need. Or Kali which is aimed at infosec professionals and is full of hacking tools, or distros that are intended for running on older computers, with less RAM and resources - like puppy and bunsenlabs which use more lightweight desktops and software.... But again, these are all cosmetic things. At the end of the day, they are all Linux.
Hope this helps!