הקורא את המגילה מברך לפניה שלש ברכו' על מקרא מגילה ושעשה נסים ושהחיינו וביום אינו חוזר ומברך שהחיינו: הגה וי"א אף ביום מברך שהחיינו [טור בשם ר"ת והרא"ש והמגיד] [וכן נוהגין בכל מדינות אלו ואחד יכול לברך ושני קורא] [הגהות אשירי פ"ב] ולאחריה נוהגים לברך הרב את ריבנו וכו' אם לא בירך לא לפניה ולא לאחריה יצא: הגה ונהגו לומר בלילה אשר הניא אבל לא ביום [כל בו וב"י בשם א"ח] ואין לברך אחריה אלא בצבור:

One who reads the Megillah recites three blessings beforehand: “al mikra Megillah,” “she’asa nissim,” and “shehecheyanu.” During the day he does not repeat the blessing shehecheyanu. Rema: Some say that even during the day one recites shehecheyanu (Tur in the name of Rabbenu Tam, the Rosh, and the Maggid), and this is the custom in all these lands; one person may recite the blessings while another reads (Hagahot Ashiri, ch. 2). Afterward it is customary to recite “Ha-rav et riveinu…” If he did not recite the blessings either before or after, he has nevertheless fulfilled his obligation. Rema: It is customary to say “Asher heni” at night but not during the day (Kol Bo; Beit Yosef in the name of Orḥot Ḥayyim), and the concluding blessing is recited only in the presence of a congregation.

One may not converse while it is being read.

Even though he has already fulfilled his obligation, he recites the blessing in order to discharge another person’s obligation.

One who is somewhat prevented and cannot go to the synagogue, and must wait until after the congregation has read, and finds it difficult to remain fasting for so long, may hear its reading while it is still day, from plag ha-minḥa and onward. Rema: however, it is forbidden to eat before hearing the reading of the Megillah, even if the fast is difficult for him (Terumat HaDeshen §109).