Selector is one of those things that you should probably learn from a good PD or MD and pass it down... that's how I learned. Sitting in for a couple days will show you "the basics"--but I have spent hours and hours tweaking Selector to do what I want, and it takes a lot of time and patience to "bend it to your will"---after all, that's why knowing Selector can be considered an advantage ;-)
The easiest way is to start with a station's database that is already functioning and then modify it from there vs. starting from scratch... but you need to get the networking connections first. I am assuming you are already at a station--so go talk to your PD! If you aren't at a station yet, work on getting in part time and learning... Selector is one of those advanced things you will eventually learn--but there are TONS of things to learn in radio first. I still learn new things every day!
As for DOS vs. Windows, RCS *still* sells the DOS version--DOS has a number of keyboard shortcuts that make navigating Selector much easier than Windows (Windows Selector is basically the DOS software with a GUI). The old pros still swear by it--and honestly, that's what I learned on, and I miss it. That said, they now have GSelector out, which is where everything is eventually going.
James