What were thee events that happened from the last day of Passover until Pentecost?

(It's "Shavuot" or "The Feast of Weeks," not "pentecost." The latter is not a name that holds any meaning for Jewish people.)

To answer the question, you only need to open the book of Exodus (ch.15-20) and read.

1) On the last day of Passover, God split the Reed Sea, and the Israelites sang praise to Him.

2) The Israelites journeyed three days, finding no water.

3) God miraculously sweetened the bitter water at Marah on the third day.

4) The Israelites came to Elim, where were twelve springs of water, and seventy palm trees.

5) On the thirtieth day after the Exodus, in the wilderness of Sin, God provided quail temporarily, and began providing manna for the entire forty years.

6) The Israelites camped at Rephidim and asked for water. God gave them water after commanding Moses to strike a rock.

7) The battle against the Amalekites.

8) Jethro came from Midian to join the Israelites.

9) At Jethro's advice, Moses chose officers/judges of the tens, fifties, hundreds and thousands.

10) The Israelites arrive at the foot of Mount Sinai in the third month after the Exodus and prepare for the Revelation of God.

11) God gives the Ten Commandments to the Israelites.