'Yog' [ from the language Hindi] literally means 'Union'. More specifically it signifies 'Union of the Self with the Divine'. There are different types of Yog (or more accurately different paths of Yog). These days people refer to Yog as [ योग ] as Yoga [ योगा ] which is a misnomer. Actually it should be called Yogah [ योगः from Sanskrit]. Yog is Hindi; Yogah is Sanskrit. Yoga is a misnomer.
The Great Indian Sage Patanjali is believed to be the founder of Yog. You can read more about his teachings in his books. Additionally more about Yog can be found in one of most popular sacred scriptures of Hinduism - The Holy Geeta.
According to Patanjali there are 8 Main types of Yog. Karm yog [ कर्म योग ], Raj Yog [ राज योग ], and Gyan Yog [ ज्ञान योग ] are among the most popular ones.
According to Shree Krishna - Karm Yog is the most superior and most important of all. You may ask why. Well, to be honest its a very important & relevant question. Fortunately for us Arjun had the intelligence to ask that question and hence we have the reply from Shree Krishna.
He said - "Karm Yog is superior to all other Yog simply because without 'Karm' the world simply can not exist. And I want to be an example to the world that every one should do their 'Karm' (duty) and that is the reason I re-incarnate myself with the help of my own 'Maya' [Divine Illusion]. Anyone doing 'Karm' is contributing to the sustenance of the world. Without 'Karm' the universe simply can not exist."
So we have his answer. Now the next question is How to be a 'Karm Yogi'. And you may also ask - "Everyone of us is doing some kind of 'Karm' [work] so aren't we all 'Karm Yogis'?
Yes we are all 'Karm Yogis'. However 'Karm' doesn't mean Work. 'Kaary' means 'Work'. 'Karm' means 'Duty'. A work that is your duty. Now basically 'Karm' is our inherent nature. We all do our 'Karm'. We just need to develop the skill to do 'Nishkaam Karm' - "Selfless Duty".
Now what is that you may ask. To put simply - its fulfillment of duties without any expectation of result or attachment to anything.
Krishna just asks us to do our Duty not because we will get something out of it but because it is our duty to do it.
For example - we work at our jobs to get hikes and promotions. I agree that result is often the driving force for doing work - so does Krishna - and that is why he's telling you - "Do Selfless Duty". Because if you're not bothered with the result and you're doing your job because it is your duty - it will make you a better person and professional. When you are not bothered about the outcome and you treat your job as your duty; you perform better.
I have seen many people who are not satisfied with their jobs. Well its human nature. We are never satisfied with what we have. That's the basic driving force for the development of the society - otherwise no innovation or development would ever take place.
However once you realize the fact that the result simply does not matter when you do your job because it is your duty you realize that you are not burdened with performance issues and you're able to focus better. You're able to concentrate on doing your job instead of concentrating on its outcome; which makes you much better at your job.
I have been trying to follow this simple principle for last 4 years and I can tell you its thrilling and its fun. I do accept that there are circumstances when I tend to forget this basic principle but by God's grace I am always reminded of it and I continue with my 'Nishkaam Karm'.
Today I am a very happy man. I am happy 50% of the times. The other 50% of the times I am very happy :D
Being happy is a natural human state. You just need to realize. Its very very simple to reach this state. And this is the state of the great sages. This is the state reached through meditation and different Aasanaas. This Karm Yog is a much easier way to attain this state.
So on this occassion of Shiv Ratri - I wish that you too succeed in achieving the Ever Happy state through 'Nishkaam Karm' - Just like Lord Shiva achieved.