Top Shavuot Sources on Sefaria

(3) It is prohibited to fast immediately after the holiday of Shavuot. Ramah: And we do not say Tachanun from the beginning of Rosh Chodesh Sivan until the 8th day, which is after the post-holiday day (Hagahot Maimoni, Hil' Tefillah Umnagim). We have the custom to spread out plants on Shavuot in the synagogue and in houses, as a memory for the happiness of the receiving of the Torah. We have a custom everywhere to eat dairy food on the first day of Shavuot. And it seems to me that the reason is: It is like the two foods that are taken on the evening of Pesach, a reminder of the Korban Pesach and a reminder of the Korban Chagiga, so too we eat a dairy food followed by a meat food, and we bring with them two loaves on the table in place of the Mizbeach, and thus there will be a reminder of the two loaves that were brought on "The day of the Bikkurim."

(12) Dairy foods - See Magen Avraham and I also heard in the name of a Gadol who said a correct reason for this: that when Bnei Yisrael stood at Har Sinai and accepted the Torah(When the 10 commandments were revealed, and through this all the parts of the Torah were also revealed to them, like that Rav Sadya Gaon writes, that the 10 commandments sustain the whole torah) and they went down from the mountain to their homes they found nothing to eat immediately except for dairy foods because for meat they would need much preparation to slaughter with a checked knife like Hashem commanded... And to clean out the strings of forbidden fats and blood, and to rinse and salt(the meat). Also to cook in new vessels because their previous vessels had been used to cook meat (that they now discovered was actually trief) had been used in the last 24 hrs (which is what is forbidden Biblically) so their old vessels were forbidden to them, therefore they choose on account of the time to eat dairy foods and we do this as a commemoration of this.

(7) "And God spoke to Moses in the Sinai Wilderness" (Numbers 1:1). Why the Sinai Wilderness? From here the sages taught that the Torah was given through three things: fire, water, and wilderness. How do we know it was given through fire? From Exodus 19:18: "And Mount Sinai was all in smoke as God had come down upon it in fire." How do we know it was given through water? As it says in Judges 5:4, "The heavens dripped and the clouds dripped water [at Sinai]." How do we know it was given through wilderness? [As it says above,] "And God spoke to Moses in the Sinai Wilderness." And why was the Torah given through these three things? Just as [fire, water, and wilderness] are free to all the inhabitants of the world, so too are the words of Torah free to them, as it says in Isaiah 55:1, "Oh, all who are thirsty, come for water... even if you have no money." Another explanation: "And God spoke to Moses in the Sinai Wilderness" — Anyone who does not make themselves ownerless like the wilderness cannot acquire the wisdom and the Torah. Therefore it says, "the Sinai Wilderness."

(4) One who ate cheese, and wants to eat meat, needs to remove from the table leftover bread that he ate with the cheese. And it is forbidden to each cheese on the tablecloth that they ate bread on. (And vice-versa is similarly forbidden.) (So is implied in the Aruch.) And all the more so is it forbidden to cut cheese, even cold, with a knife that they usually use to cut meat. And not only that, but even the bread that they eat with the cheese is forbidden to cut with a knife that they use to cut meat. And vice-versa is also similarly forbidden. However, via stabbing into hard ground, it is permitted. (Beit Yosef, quoting A"Ch and Kol Bo). But, all of Israel already is accustomed to having two knives and to mark one of them, so it is distinguished, they are accustomed to marking the dairy one, and it's not right to change a custom of Israel.