Leviticus 23:10-14King James Version (KJV)
10 Speak unto the children of Israel, and say unto them, When ye be come into the land which I give unto you, and shall reap the harvest thereof, then ye shall bring a sheaf of the firstfruits of your harvest unto the priest:11 And he shall wave the sheaf before the LORD, to be accepted for you: on the morrow after the sabbath the priest shall wave it.12 And ye shall offer that day when ye wave the sheaf an he lamb without blemish of the first year for a burnt offering unto the LORD.13 And the meat offering thereof shall be two tenth deals of fine flour mingled with oil, an offering made by fire unto the LORD for a sweet savour: and the drink offering thereof shall be of wine, the fourth part of an hin.14 And ye shall eat neither bread, nor parched corn, nor green ears, until the selfsame day that ye have brought an offering unto your God: it shall be a statute for ever throughout your generations in all your dwellings.
Leviticus 23:4-6King James Version (KJV)
4 These are the feasts of the LORD, even holy convocations, which ye shall proclaim in their seasons.5 In the fourteenth day of the first month at even is the LORD's passover.6 And on the fifteenth day of the same month is the feast of unleavened bread unto the LORD: seven days ye must eat unleavened bread.
The fourteenth of the first month which is Aviv used to be Nisan is in the spring and the first harvest called first fruits was usually cereals mainly barley and some wheat but the large wheat harvest was in the second harvest. The Sabbath here is the seven day Sabbath following the Passover, and the waving of the sheaf is the day after that, which would be the first day of the week and it also started the counting of the weeks of seven Sabbaths the day after would be the fiftieth day and the Feast of Weeks or Pentecost which also means fifty. The main thing of the Sheaf offering they could not eat any of the grains before the priest waved it unto the Lord.
The chapter 23 of Leviticus covers the appointed feasts. The Jewish encyclopedia is a place you can check out and has information may help. Oh by the way, Jesus resurrected the first day after the Sabbath after the Passover same day of the waving of the sheaf which is called the first fruits which falls inside the seven day feast of unleavened bread.
Passover the 14th form year to year changes to what day of week it falls on. The Feast of Weeks is the first day after the 49th day or seven Sabbaths Sunday to us, so the First fruits is on the first day of the week. So it would be the first day after the weekly 7th day Sabbath after the Passover inside the 7 day Feast of Unleavened bread.