Praise be to Allah and prayers and peace be upon the Messenger of Allah and upon his family and companions. The manner of performing the Prayer of Istikhara is explained by the Messenger of Allah (peace be upon him). He reported that Jabir ibn Abdullah (may Allah be pleased with him) said: The Messenger of Allah (peace be upon him) taught us to perform Istikhara in all matters just as he taught us a Surah from the Quran. He said: If one of you intends to do something, let him pray two voluntary rak'ahs without the obligatory prayer, and then let him say: O Allah, I seek guidance from You with Your knowledge, and I seek ability from You with Your power, and I ask You from Your great favor, for You are able and I am not able, and You know and I do not know, and You are the Knower of the unseen. O Allah, if You know that this matter is better for me in my religion, my livelihood and the outcome of my matter, then ordain it for me and make it easy for me, and bless me in it. And if You know that this matter is worse for me in my religion, my livelihood, and the outcome of my matter, then turn it away from me and turn me away from it, and ordain for me the good wherever it may be, and may I be pleased with it. Then he should mention his need when he says: O Allah, if you know that traveling or marrying so-and-so is good for me... then state your need. The Istikhara prayer is recommended for the servant if a worldly matter arises that he is permitted to do. There is no Istikhara in a mandatory act or a recommended act because he is commanded to do them without seeking guidance, nor is there Istikhara for prohibited and disliked actions because he is commanded to refrain from them without seeking guidance. The Prayer of Istikhara consists of two independent rak'ahs which can be prayed at any time except during the disliked times which are: after the 'Asr prayer until sunset, after the Fajr prayer until sunrise, and just before noon when the sun is at its zenith except if there arises an urgent need, then he may pray it after the two rak'ahs, making supplications as was narrated in the previous hadith. It is allowed to supplicate with it before the Tasleem from the two rak'ahs, and it is permissible to supplicate with it after the Tasleem, as for supplication in general, Allah said: "And your Lord says, 'Call upon Me; I will respond to you' [Ghafir: 60]. And He also said: "Invoke your Lord in humility and in secrecy; indeed, He does not like transgressors" [Al-A'raf: 55]. And He said: "And when My servants ask you concerning Me, indeed, I am near. I respond to the invocation of the supplicant when he calls upon Me" [Al-Baqarah: 186]. And He said: "And is there anyone who answers the distressed when he calls upon Him and removes evil?" [An-Naml: 62]. It was narrated by Al-Tirmidhi and Abu Dawood on the authority of Al-Nu'man ibn Bashir (may Allah be pleased with them) from the Prophet (peace be upon him) who said: "Supplication is worship". The chapter of supplication is vast, and you can refer to the book Riyaaḍ al-Ṣāliḥīn (the chapter on supplication) or other books which include authentic supplications and remembrances. And Allah knows best.