In BattleKnight, you can choose to "work" for an allotted time. You can work up to 8 hours, 12 if you have a premium account.
There are three different types of work: one has the best silver return but without any karma reward; the others with less silver but with either good or evil karma.
Different locations have different work descriptions as well as work types; the location Grand only has work without karma, while Tarant has all three.
While you are working, you cannot travel, fight in the arena, or go on missions.
Once the amount of time you have chosen to work is over, you can collect your silver and/or karma. Before that time, however, you cannot. You can still cancel the work, but you will not get anything for it.