Gita meaning

 नमस्ते। 

मम नाम शिवः। अहं राधाकृष्णमहोदयस्य L1 वर्गे पठामि। अधुना अहं गीतातः श्लोकत्रयं तस्य अर्थं च वदामि।

श्रीभगवानुवाच |
लोकेऽस्मिन्द्विविधा निष्ठा पुरा प्रोक्ता मयानघ |
ज्ञानयोगेन साङ्ख्यानां कर्मयोगेन योगिनाम् || 3.03||

Lord is answering arjuna's confusion about lord's advice about both knowledge as well as practice karma yoga. So he asks the one way to achieve supreme goodness.

The lord says: Oh faultless one, in this world of mine, a two fold 'ways of life' have been defined by me , right from the begnning 

These are 

a. jnanayoga (the way of life purely dedicated to knowledge in the form of physical sanyasa) for the sanyasis 

b. karmayoga (the way of life for those who are householders)

योगस्थ: कुरु कर्माणि सङ्गं त्यक्त्वा धनञ्जय |
सिद्ध्यसिद्ध्यो: समो भूत्वा समत्वं योग उच्यते || 2.48||

48. Oh Arjuna! Abiding in Yōga, giving up attachment and remaining the same in success and failure, perform actions. Equanimity is called Yōga. 

lord advises Arjuna act to in the world, by having proper-attitude towards material gain by making it subservient to inner growth so that material gain and material loss will not create a big turmoil in the mind.

This mental balance because of the appropriate focus on inner growth is called Samatvam. 

Therefore, Kṛṣṇa says, samatvam yōgaḥ ucyatē. The one who values the inner-growth more than external-accomplishment and therefore the consequent mental balance. 

There is no question of riskless life and therefore you have to take risk but at the same time have the mental balance. So yōgasthaḥ karmāṇi kuru.

How? saṅgaṃ-tyaktvā, shifting the attachment from material-growth to spiritual- and inner-growth. Saṅga means attachment; here attachment is attachment to the material gain. 

And what about attachment to spiritual-growth? 

siddhyasiddhyōḥ samō bhūtvā. Be equanimous both in success and failure by enjoying the appropriate attitude towards them. So siddhi means success; asiddhi means failure; towards both maintain equanimity. Because first definition of karma-yōga is samatvam yōgaḥ ucyatē. It is not any particular action, but it is particular state of mind that is called karma-yōga. Therefore Arjuna you be a karma-yōgi. 

बुद्धियुक्तो जहातीह उभे सुकृतदुष्कृते |
तस्माद्योगाय युज्यस्व योग: कर्मसु कौशलम् || 2.50||

buddhiyuktaḥ, means a karma-yōgi, who has got a proper buddhi; means proper attitude as we saw in the last sloka.

sukṛta-duṣkṛtē jahāti : lord says because Every karma-yōgi will come to jñāna-yōga one day or the other; and once he comes to jñāna-yōga and discovers his true nature, then he transcends all the karma-phalās; 

, tasmādyōgāya yujyasva. But to come to that jñānam, now you have to do action. You cannot say that I will leave everything now itself for sanyasa.

yōgaḥ karmasu kauśalam. skill in action; is karma-yōga

Here by the word skill, Kṛṣṇa does not mean expertise in the performance-of-action; anybody can be a skillful-expert if only he repeats the action again and again; like making coffeee

Śankarācārya gives a beautiful definition; NOT by changing-the-action, but by changing-the-attitude.

Therefore, skill is conversion of binding-actions into liberating-actions, by a change of attitude.

To summarize  karma yoga is 

yogah karmasu koushalam: performing dharmic actions (such as natural duties) as a form of dedication to lord

samatvam yogah uchyate: accepting results as a prasada from lord who alone controls the results for action