Sankashti Chaturthi

Sankashti Chaturthi is also known as the Sankata Hara Cahturthi , A chaturthi falling on the Krishna Paksha(the waning moon phase) of every month is called as a Sankashti Chaturthi. This is considered as an auspicious day for worshipping Lord Ganesha.

The Chaturthi thithi  of Krishna Paksha(fourth day of the waning moon phase) is a special day for the devotees of Ganesha. Lord Ganesh would shower his blessings on anyone who observes the Sankashti Chaturthi vrat or worship him on this day.  Sankasthi Chaturthi is as good a auspicious day as  is t Ekadashi(the 11th day of both the waxing and waning moon) for the  devotees of  Lord Vishnu and Masa Shivaratri(Thirteenth day of the waning moon) for the devotees of Shiva

The name Sankata Hara means :

Sanakata means immense trouble

Hara means removed

and the name itself suggests that one who observes the Sankashti Chaturthi vrat would be moved out of all the troubles he is in and would lead a happy life.

 Sankashti Chaturthi vrat

This is a simple Vrat same as the Ekadashi Vrat, where people observe fast on this day until evening and would eat only after looking at the moon and once their pooja (worship) to Lord Ganesha is done.
The pooja would comprise of the normal Ganapati pooja, then a pooja with Druva Grass which is dearer to Lord Ganesha. Then an offering comprising of food items  like Modak, laddu etc that are a favourite of Lord Ganesha are made.

On this day as a part of pooja the following are recited:

Sankashta Nasana Sthotra

Vinayaka Ashtothara Sethanamavali

Or Vinayaka Sahasranama Sthothram

The returns  of doing this vrat is explained in a story of Sankashti Chaturthi vrat katha or story.