'Gravure' printing involves printing from an engraved plate.
The one on the left is probably litho. There is insufficient detail to warrant gravure.
Bank notes are typically printed gravure.
Postage stamps are mostly printed litho.

The one on the right is as Berry says, 4 color process. Imagine the modern day computerised printing presses as being highly sophisticated laser or dot matrix printers. Works pretty much the same way I believe.