What is the purpose of a heart stent and how is it administered.?

Open narrow coronary: Stents provide a scaffold to open a narrowed coronary artery. It is delivered typically via femoral artery or sometimes via radial or brachial artery.

To open blockages: Most commonly "heart stents" are placed in the coronary arteries, the main blood vessels that feed the heart, because there are blockages which impair the efficient flow of blood to the heart muscle. These are delivered through tiny plastic tubes, called catheters, placed through a small needle puncture in the groin or in the arm. This is done under x-ray guidance.

Besides just opening a clogged artery like others have said, a stent was specifically designed to prevent the collapse of an artery opened by a balloon angioplasty, and to prevent it from re-clogging with scar tissue, especially the drug-eluding stents. They are put in by crimping them down on a balloon and then inflating the balloon to expand. I hope this answers your question more accurately.