Ganesha , also spelled Ganesa or Ganesh, also known as Ganapati, Vinayaka is one of the deities best-known and most widely worshipped in the Hindu pantheon.
Ganesha’s elephant head makes him particularly easy to identify. Ganesha is widely revered as the Remover of Obstacles and more generally as Lord of Beginnings and Lord of Obstacles (Vighnesha, Vighneshvara ), patron of arts and sciences, and the deva of intellect and wisdom. He is honoured at the beginning of rituals and ceremonies and invoked as Patron of Letters during writing sessions.
The name Ganesha is a Sanskrit compound, joining the words gana meaning a group, multitude, or categorical system and isha meaning lord or master. Vinayaka is a common name for Ganesha that appears in the Puranas and in Buddhist Tantras. This name is reflected in the naming of the eight famous Ganesha temples in Maharashtra known as the Ashtavinayak.
Ganesha was born with a human head and body and that Shiva beheaded him when Ganesha came between Shiva and Parvati. Shiva then replaced Ganesha’s original head with that of an elephant.
Ganesha is considered to be the Lord of letters and learning. In Sanskrit, the word buddhi is a feminine noun that is variously translated as intelligence, wisdom, or intellect. The concept of buddhi is closely associated with the personality of Ganesha, especially in the Puranic period, when many stories stress his cleverness and love of intelligence. One of Ganesha’s names in the Ganesha Purana and the Ganesha Sahasranama is Buddhipriya. This name also appears in a list of 21 names at the end of the Ganesha Sahasranama that Ganesha says are especially important. The word priya can mean “fond of”, and in a marital context it can mean “lover” or “husband”, so the name may mean either “Fond of Intelligence” or “Buddhi’s Husband“.
Ganesha is identified with the Hindu mantra Aum.
Devotees offer Ganesha sweets such as modaka and small sweet balls (laddus). He is often shown carrying a bowl of sweets, called a modakapatra
Festivals associated with Ganesh are Ganesh Chaturthi or Vinayaka Chaturthi in the suklapaksa (the fourth day of the waxing moon) in the month of bhadrapada (August/September) and the Ganesa jayanti (Ganesa’s birthday) celebrated on the cathurthi of the suklapaksa (fourth day of the waxing moon) in the month of magha (January/February).
Sources : wikipedia & different online websites.