In plain words
One who is heroic in action is a 'karma-yogi'; one who follows the path of Prema is a 'bhakti-yogi'; the seeker of inner power is a 'raja-yogi'; and the seeker on the path of philosophical truth is a 'jñāna-yogi'. The term 'yogi' applies to all four of these categories, and in Bharat's own supreme teaching, these four kinds of yogis are held to be the principal ones.
The first, karma-yoga, is the path that unites one with God through the performance of action. We constantly see, in this world, countless people who seem to have been born for the sake of some particular action or other; their intellect never settles at all in the field of contemplation, and only activity that can be directly seen occupies their minds entirely. For the lives of such people too, surely, there must be some discipline that serves them! In this world, all human beings keep performing some action or other, but, not knowing the secret of action, we largely end up wasting our own true natures. Karma-yoga teaches exactly this secret: where, when, and how ought action to be performed? Karma-yoga teaches how to employ the greatest portion of our strength toward accomplishing the task at hand, so that the greatest result may follow from it. But here we must also carefully note an important objection: that distress itself arises through the performance of action. Attachment alone is the cause of all the afflictions that befall the mind and body. I myself am fond of performing action, and I long to do good to someone — but there is every chance that he may forget that good deed and, instead, do me harm in return. Should that happen, distress of mind arises in me. This kind of fear becomes something of a hindrance to the performance of action; it ruins both one's zeal for action and one's very capacity for it. Without ever asking whom it helps or how it helps, karma-yoga firmly teaches that one should act for the sake of action alone. What, then, is the reason that the karma-yogi remains absorbed in the performance of action? It is simply his own nature; it is his own true benefit,