What are the Sunnahs of urination, and how is purification from it performed? What are Istinja', Istibra', and Istijmar, how are they performed, and is performing them obligatory?

Istinja (cleansing with water), Istijmar (cleansing with stones), and Istibra (ensuring discharge has ceased):

Istinja is the removal of impurities discharged from the two private parts (front and back) using water or a stone. Istijmar is the use of stones or similar materials to remove impurities from the two private parts. Istibra is the act of ensuring that no more discharge is coming out, by coughing or walking.

Reason for the names:

Istinja comes from "najawtu ash-shajarah," meaning "I cut the tree," or from "an-najwah," meaning "a raised piece of land." Istijmar comes from "al-jimār," which are small stones.

Ruling on Istinja:

It is obligatory according to the majority of scholars for every impure and contaminating discharge from either of the two private parts, and it is a condition for the validity of prayer.

Etiquettes of relieving oneself and performing Istinja:

Removing the impurity with the left hand, preparing the cleansing agent, using solid materials an odd number of times, giving precedence to the front over the back, staying away from shaded areas and stagnant water, not facing or turning one's back to the Qiblah, not uncovering one's private parts except when close to the ground, reciting the supplication upon entering and exiting (the restroom), striving to perform Istibra thoroughly, and water is better than stones.