The Constituent Assembly was formed in 1946, with Dr B R Ambedkar chairing the drafting committee. The Constitution was adopted on 26 November 1949 and came into force on 26 January 1950.
The Preamble declares India a sovereign, socialist, secular, democratic republic; the words socialist and secular were added by the 42nd Amendment in 1976. The Preamble is not enforceable in court but guides interpretation.
Structurally the Constitution has parts, schedules and articles. Part III covers Fundamental Rights, Part IV the Directive Principles and Part IVA the Fundamental Duties, added by the 42nd Amendment.