The (Indian) Republic is governed in terms of the Constitution of India which was adopted by the Constituent Assembly on 26th November 1949 and came into force on 26th January 1950.
A republic is a state under a form of government in which the people, or some significant portion of them, retain supreme control over the government.
Take a moment to read some of the best about Republic day and what it means
Are we republicans or democrats : Harsh gupta on the Republic of India.
You can download a pdf copy of a photolithographic reproduction of the Constitution of India from the World Digital Library [PDF]. Pages from the book are shown below.
January 26 was selected because it was the day the Purna Swaraj declaration (Declaration of the Independence of India) was promulgated by the Indian National Congress at Lahore in 1930. In fact, the Congress had then asked the people of India to observe January 26 as Independence Day. Moreover, Republic Day is also about the Indian constitution, which was a wholly Indian enterprise.
Republic Day, on a date we ourselves chose, ought to be the more solemn occasion — a day of promises to make and pledges to keep.
If Independence Day is about the remembrances and retrospection, Republic Day ought to signify how we can preserve and improve the fate of the country, and how that task falls upon us, each one of us.
You could read more at Pragmatic Euophony on the Republic day
And as the author suggests, remember that the Republic day is for renewing the fire inside to fight for a free, equal and truly republic-an India.
You could take up this year to learn more about how the problems in india can be solved, and I would say there is no better book than Breaking free of Nehru, and no better company than the Freedom Team of India to keep.
To a Free India.