Kernel is the very core of the system, and in this case, it tells you the version of Linux you have and who modified it, FC39 is Fedora Core 399, Packages are all the stuff installed in your system, each being a type of package, Shell is what you use to communicate with that Kernel, so you are using bash, which is basically the standard, Terminal is what you use to communicate with the kernel, a terminal was a dumb pc in the good old days (tho it's still being used) that you used to communicate to a real PC, so that's what basically is right now