Software on different distros/DE

Newbie here.I'm confused about the difference in software managers and what will run on what.Does a program only work for distro/DE it's was written for like a Debian or Ubuntu based distro? And/or DE like GNOME or KDE. And will say GNOTE run in KDE? And what's the difference between the software managers? Are there ones that are better then others for the distros and what their based on? And last whats the difference/advantages/disadvantages between Flatpak and Snap. I've heard the software in Flatpak is more secure. Thanks