Yosef Karo

“ The mitzvah is for each individual to count for himself. One should count standing, and recite a blessing first. The days and weeks are counted. How? On the first day one says: "Today it is one day (in the Omer) ," until seven days are reached; then he says: "Today it is seven days that are one week (in the Omer) ." On the eighth day one says: "Today it is eight days that are one week and one day (in the Omer) ," and so on till fourteen days are reached. [Then] one says: "Today it is fourteen days that are two weeks (in the Omer) ." In this manner one goes on counting, up to forty-nine days. ”

“ The painstaking ones do not count until the appearance of the stars; and this practice should be followed.
סעיף ב אם טעו ביום המעונן ובירכו על ספירת העומר חוזרים לספור כשתחשך והמדקדקים אינם סופרים עד צאת הכוכבים וכן ראוי לעשות:
489:3 One who prays [Ma'ariv] with the congregation when it is still day, counts with them without a blessing; and if he remembers at night, he should recite the blessing and count. Rema: Even if he answered Amen after the blessing of the congregation, if he intended not to fulfil the obligation, he should again bless and count at night (Beit Yoseph citing Rashba) . ”

“ If one has no wine and needs to make the Yakneha"z kiddush, see siman 296 above.
סעיף ט ליל שבת וליל יום טוב, מברכים וסופרים אחר קידוש בבית הכנסת. ובמוצאי שבת ויום טוב, קודם הבדלה, אחר קדיש תתקבל. וכשחל יום טוב האחרון של פסח במוצאי שבת, דאז אומר קידוש והבדלה בפעם אחת, יש לספור קודם שמברכין על הכוס בבית הכנסת. הגה: ואם אין לו יין וצריך לקדש יקנה"ז, עיין לעיל סימן רצ"ו.
489:10 It is forbidden to eat chadash ("new [grain] produce") even nowadays, whether in form of bread, roasted grain, or fresh grain, until the beginning of the 18th of Nissan's night ”