The separation process can be very simple to extremely complex. If you are separating spot color vector artwork for printing on a white shirt. It can be very simple. The Other extreme is simulated process on dark shirts. There are third party rips and plugins that automate the process but they are far from perfect and a working knowledge of manually separating files is required to deal with all but the simplest files. Screenprinting institute has some dvd tutorials as well as their plugins and rips. Great dane Graphics is another. Their are others but I recomend you get a basic sep tutorial first. Sorry I couldn't give you a more cut and dry answer. but this industry is one of the few that has not been automated and streamlined, it still has an artisan type of culture. Thats the reason direct to garment is being promoted so heavily.