Here is your short paragraph on Guru Purnima:
In honour of Vyasmuni, who is revered as the supreme Guru, Guru Purnima is observed on the full-moon day in the month of Asad (July—July).
He is being credited with the work of editing all the four Vedas and has also written Mahabharata epic and many other sacred scriptures. He is being remembered on this day in an attitude of gratitude and is worshipped by performing Vyas Puja.
Asad Purnima heralds the Chaturmas or the setting in of the eagerly awaited rains that last for four month. It is said to be meritorious, if one live on milk and fruits on this day and practice vigorous Japa and Dhyan, study Brahmasutra. To utter Guru Mantra or Ishta Mantra during the Chaturmas is highly recommended.