Its Ruling and Virtue

Salatul Witr is an emphatic Sunnah. The Prophet ﷺ said: “Indeed Allah is Witr (i.e. One) and loves odd numbers of things, so observe the odd numbered Salat (i.e. the Salatul Witr), O’ people of the Qur’an.” [ Source: Abu Dawud.]
Furthermore the Prophet ﷺ used to be consistent in praying it, whether he was at home or traveling.
Description of Salatul Witr

1- The least number of raka’t of Salatul Witr is one, and the highest number is eleven or thirteen. They should be observed as two raka’at at a time with one rak’ah at the end, to make it odd.
2- The least number of raka’t of the more perfect form of Witr is three raka’at, thus: He first observes two raka’at and says at-Tasleem, then the remaining one rak’ah is said and at-Tasleem is also said to round up the Witr. The three raka’at can also be said together with just one at-Tashahud.: It is recommended to recite suratul al-A‘la after Fatiha in the first rak’ah, and in the second rak’ah, suratul al-Kafirun, while in the third, suratul al-Ikhlas.
This was authentically reported from Ubayy bn Ka’b t,, who said: The Prophet ﷺ used to recite, in the first rak’ah of Salatul Witr, “Sabbihisma Rabbikal ‘Ala” and in the second; “Qul-Ya Ayyuhal Kafirun” and in the third; “Qul Huwa llahu Ahad.” [ Source: An-Nasai.]
Time of Salatul Witr

From after ‘Isha’ prayer until the appearance of the Dawn (Fajr). Observing it is best in the last third of the night. This is due to the statement of the Prophet ﷺ “Indeed the Salat in the last part of the night is witnessed,” in the hadeeth: “Whoever hopes to get up at the end of the night, let him make Witr at the end of the night; for indeed the Salat in the last part of the night is witnessed, and that is better.” [ Source: Muslim.]
Moreover, he should not repeat Witr in the same night; due to the Prophet’s saying: “There are no two Witrs in one night.” [ Source: Abu Dawud.]
The Supplication of Witr

It is permissible to supplicate in the last rak’ah of Witr before [ Source: Abu Dawud.] or after rising from bowing [ Source: Al-Bukhari.].
The hands are raised and supplications (reported from the Prophet) are said. For example: “Allahummahdini fiman hadayta, wa ‘aafini fiman ‘aafaita, wa tawal-lani fiman tawallaita, wa baarik li fima a’ataita, wa qini sharra ma qadaita, fa innaka taqdhi wa la yuqdha ‘alaika, innahu la yadhillu man walaita wala ya ‘izzu man ‘aadaita tabaarakta Rabbana wata ‘alaita.”Meaning: “Oh Allah, guide me along with those whom You have guided, pardon me along with those whom You have pardoned, be an ally to me along with those whom You are an ally to and bless for me that which You have bestowed on me and protect me against the evil of what you have decreed. For verily, You order and none can order You. For surely, he whom You show allegiance to is never abashed and he whom You take as an enemy is never honored. O’ our Lord, Blessed and exalted are You.” [ Source: At-Tirmidhi.]