Does this require you, like old-tech CNC machines, to know CNC stuff?
Or can I just put metal blocks into it and pull out parts I want?
You need to know "CNC stuff".
Of course, the additive manufacturing/3D printing, you need to know quite a bit too. But the one huge advantage, besides the ability to make shapes and voids that CNC/subtractive can't is that it does not require absolute accurate positioning relative to the feedstock, the printing only needs to be accurate relative to it's own starting point and nothing else.
Within reason of course, you can't have your part start so off center the print extruder runs out of room in the printable volume it can work in, but you get the idea.
The CNC process, the fitment of the blank or block of raw material matters. And depending on the complexity of the CNC mill and that of the part you are trying to produce, you may have to rotate the part and position it accurately in the machine several times to give the milling bits extra access to remove material from different direction.
The seeds of the 3D printing revolution were really sown way back when cheap 1000+ DPI ink-jet printing became a commodity product. All it's really doing is using a different print material, and adding a third axis of operation. Multi-tool, multi-axis CNC mills with extra degrees of freedom for the tools and the mounting for the work-piece being made that reduce the needed input from a human operator are certainly out there, but they are expensive, and require precise tolerances and clearances in their parts, lots of strong parts etc.
