Instead of painstakingly assigning jobs to dwarves in a very fine grained process through the labor menu for each individual, dwarves are assigned to jobs.

That is, the vast majority of jobs are by default assigned to all dwarves, and the game intelligently assigns work based on dwarf skill and pathing distance. You are free to tweak labor settings from there, for instance by assigning a forge to be the exclusive workplace of a legendary weaponsmith and only making weapons at that forge, or specializing miners to only mine so that they won't find themselves cleaning fish when idle between mining gigs. You can also create custom work profiles more akin to the old setup, enabling or disabling specific tasks and then assign that profile to specific dwarves if you want to get so detailed. However I find the new system works very well.