Anantha Vratam, also known as Ananta Chaturdasi or Anandapadmanabha Vrat, is dedicated to Lord Vishnu. In 2013, the date of Ananta Vratam is September 18. It is believed that Lord Vishnu appeared in the form of Anandapadmanabha sleeping on the serpent Ananta – the famous Ananta Shayana form. The main ritual on the day is the tying of a sacred thread known as Ananta Daram.
The observance of Ananta Vrata is believed to rid one from all sorrows. Escape from sorrow is not possible by merely performing rituals. But by realizing what Ananta Shayana symbol represents. Meditating on the symbolism represented in Sri Narayana in yoga-nidra on a great serpent bed (Ananta). It is for each person to realize the symbolism. Rituals are just an initial step in the long journey of self realization.
You can find more details about how to observe the Anantha Vratam in this post.