Short about printing
The printing era has been pretty good since Gutenberg. First, important things were printed like books. But these are REALLY important, not some literature for the mob. Well, because the mob was quite illiterate at the time. Then also such fiction was printed, meaning for the reading of the book. Well, since the last 50 years (even hundreds of them), it's all about printing - books, leaflets, business cards, even shirts, mugs, pens ... Well, really everything. Because you need to build brand awareness at the customer, i.e. printing and marketing is an inseparable couple. Because you can print everything on your T-shirt and have it originally. Well, who would prohibit the rich?
About printing companies
Paints, inks, paper, toners, foils and other consumables - these are things that can not be missing from printing plants. They are ordered wholesale and also consumed in bulk. For each order, the production costs are optimized, and the appropriate technique and type of printing is selected.
Graphic designers, DTP operators and printers deal with this. They are responsible for the quality of the printout and as soon as something is wrong they are the first to be targeted by the dissatisfied boss. Their work is quite hard and I have to admit that you have to really have a fuss to do it. Work after hours, maximum focus and responsibility - definitely not work for everyone.
DTP work programs
There are more and more graphics processing programs, from the most popular Photoshop to less known and free ones like Inkscape. Professionals usually use one or two proven programs, which translates into their high productivity.
In the work of graphics or DTP operator you usually need a program for processing vector and raster graphics. You can also include word processors, programs provided by print equipment manufacturers, to the pool of programs needed for such work.