The primary function of the parliament is to make laws for the governance of the country. It has exclusive powers to make laws on the subjects enumerated in the Union List and on the residuary subjects (that is, subjects not listed in any of the three lists). 

With regard to the concurrent list, the Parliament has overriding powers, that is, the law of Parliament prevails over the law of the state legislature in case of a conflict between the two. 

Further Reading:

• Lok Sabha
• Rajya Sabha

To read more about the Functions of the Parliament, check the linked article.