In addition to the above:
1) The Synaptic package manager is a graphical front-end to the apt-get command.
2) apt-get was originally developed for the Debian distribution and many years ago it could only handle .deb packages.
3) There is, however, a version of it (that's often called apt-rpm or apt4rpm) that can handle .rpm packages. So neither apt-get nor Synaptic is a tool that can only be used in Debian and its derivatives.
Just adding a bit, from my memory: apt-get was ported to RPM systems, if memory serves me well, by Alfredo Kojima(who also created Synaptic), from the now deceased Conectiva from Brazil(yes, Brazil has some tradition on open source).
He also created Windowmaker( a rather weird desktop environment, but I will try it someday).
I would say commands like rpm -i or apt-get install are, often safe, if you are in the official repos. Sometimes, when I know the package, I just install it by the cli. But I know what I am doing. People new to Linux, PCLOS, or the apt-get stuff should prefer Synaptic.