What does the Gita say about karma?

कर्मण्येवाधिकारस्ते मा फलेषु कदाचन ।
मा कर्मफलहेतुर्भूर्मा ते सङ्गोऽस्त्वकर्मणि ॥

karmaṇy evādhikāras te mā phaleṣu kadācana
mā karma-phala-hetur bhūr mā te saṅgo 'stv akarmaṇi

Your business is with action alone, not by any means with fruit. Let not the fruit of action be your motive to action. Let not your attachment be fixed on inaction.

नियतं कुरु कर्म त्वं कर्म ज्यायो ह्यकर्मणः ।
शरीरयात्रापि च ते न प्रसिध्येदकर्मणः ॥

niyataṃ kuru karma tvaṃ karma jyāyo hy akarmaṇaḥ
śarīrayātrāpi ca te na prasidhyed akarmaṇaḥ

Perform your prescribed duty, for action is better than inaction. Even the maintenance of your body would be impossible without action.

तस्मादसक्तः सततं कार्यं कर्म समाचर ।
असक्तो ह्याचरन्कर्म परमाप्नोति पूरुषः ॥

tasmād asaktaḥ satataṃ kāryaṃ karma samācara
asakto hy ācaran karma param āpnoti pūruṣaḥ

Therefore, always perform your duty without attachment, for by acting without attachment one attains the Supreme.

कर्मणो ह्यपि बोद्धव्यं बोद्धव्यं च विकर्मणः ।
अकर्मणश्च बोद्धव्यं गहना कर्मणो गतिः ॥

karmaṇo hy api boddhavyaṃ boddhavyaṃ ca vikarmaṇaḥ
akarmaṇaś ca boddhavyaṃ gahanā karmaṇo gatiḥ

One must possess knowledge about action; one must also possess knowledge about prohibited action; and again one must possess knowledge about inaction. The truth regarding action is abstruse.