Nishkama karma means selfless action: doing what needs to be done without craving for the results. The phrase may sound unfamiliar, but the experience is common. We feel it when we are fully absorbed in helping someone, cooking a meal or finishing a task for its own sake, and not worrying about reward. The Gita presents this as a skill that can be practised in ordinary work.
The classic statement is Gita 2.47: you have a right to your action, never to its fruits, so focus on duty without making results the motive and without slipping into inaction. Gita 2.38 adds acting with an equal mind in gain and loss, victory and defeat, and Gita 4.20 says freedom comes when actions are performed without dependence on results. Gita 6.1 says true renunciation is not abandoning action but doing one's duty without attachment to its results.
The Gita adds attitudes that make this possible. Gita 4.22 says contentment, freedom from jealousy and equanimity protect a person from karmic bondage, and Gita 4.14 says freedom from attachment to results prevents actions from creating bondage. Gita 3.30 asks us to offer every action and act free from craving and anxiety, and Gita 11.33 asks us to act fully as an instrument, without carrying the burden of controlling every outcome.