कृषिगौरक्ष्यवाणिज्यं वैश्यकर्म स्वभावजम्। परिचर्यात्मकं कर्म शूद्रस्यापि स्वभावजम् ॥

kṛiṣhi-gau-rakṣhya-vāṇijyaṁ vaiśhya-karma svabhāva-jam paricharyātmakaṁ karma śhūdrasyāpi svabhāva-jam

Ploughing, protection of kine, and trade are the Vaishya duty, born of his own nature. Action of the nature of service is the Shûdra duty, born of his own nature.

In plain words: Krishna says the natural work of a Vaishya is farming, caring for cows and trade. The natural work of a Shudra is serving others.