A dwarf's labor preferences define the tasks/jobs that he or she is allowed to do, whether it is food hauling, mining, hunting, or any of dozens of other tasks. For instance, only a dwarf with the wood cutting labor enabled will cut down trees whenever trees are designated to be cut.
Note that a labor is not a "job", nor a "skill". A job is the actual task of doing something, and a skill is the experience that determines how fast a job gets done, and/or the quality of any finished product (specifics vary with skill/job), while a labor preference simply designates whether a dwarf is allowed do that sort of job or not. You can view a list of all current, queued, and suspended jobs on the obs menu. A list of what job each dwarf is currently performing is visible on the nits menu.
Once designated as a labor preference, a single skill can possibly be applied to many different jobs. For instance, a dwarf with the bone carving labor designated might carve a totem out of a skull, craft bone practice bolts for a crossbow, create bone armor, or carve bone crafts to trade. Each of these is a different possible job allowed by designating the associated labor, which in each of these cases is governed by the "bone carving" skill.
Note that many labor preferences, especially hauling, have no associated skill, do not generate experience, and do not improve with practice.
The mining, wood cutting, and hunting labors require the dwarf to either pick up and wield a pick, battle axe, or crossbow. For this reason, a dwarf cannot be assigned to any combination of mining, wood cutting, or hunting at the same time. Additionally, the assignment of these tools overrides any uniform assigned to a dwarf's squad, so military dwarves should never be assigned any of the aforementioned labors.
 Viewing labors
To change a dwarf's labor preferences, access the labor screen byiewing the dwarf, then select references and abor. Use and to move the cursor up and down to hilight different categories or skills to enable or disable.
Usingcan help you locate dwarves. Select a dwarf, hit for "zoom to creature" and you'll automatically be placed in view mode on that dwarf. Use - to get to the labor configuration menu.
A category is dark gray if there are no labors under it enabled, light gray if there are some jobs enabled, and white if all jobs are enabled. (These distinctions can sometimes be very hard to tell apart in the default color scheme.)