The name of the Book of Numbers comes from the census of the people at the start of their journey to Canaan (Chapters 1-4), and the second census (Chapter 26) of the next generation as they prepared to enter the Promised Land. The first part of the Book (Chapters 1-25) recounts the rebelliousness of the first generation, who refused to follow God's leading. The second part (chapters 26-36) relates how the next generation, under the leadership of Moses and the two faithful leaders Joshua and Caleb, conquered the lands to the East of the Jordan and prepared to enter Canaan.

Numbers 1:18 - "by their polls" means "by their heads" ie. a head-count.
Numbers, chapter 6 - Nazirites were consecrated to God for a period of time, or for a life-time, either of their own free-will or by a parent's vow (Samson, probably Samuel)
Numbers, chapter 7 - imagine yourself as one of the Israelites, and picture the 12 days of festivities as the tabernacle and the Altar were consecrated to God's service. Picture the richness of the gold offerrings, and the joy of the communion feasts as Priests, Levites, and worshippers joined in cooking and eating the Peace Offerrings (For a Peace Offerring, only the fat, the kidneys, and few other parts of the animals were burned on the Altar - the rest was eaten in the presence of God. - Leviticus, chapter 3)
Numbers 11:33 - The Israelites saw God as being in control of everything, therefore the ultimate cause of everything; so they counted Him as allowing what was probably death by gorging on unaccustomed rich food.
Numbers 12:1 - Moses' marriage to an Ethiopian woman - it is not known whether Zipporah was still living, but the main cause for complaint seems not to be Moses' marriage, but that Miriam was jealous of her younger brother.
Numbers 20:10 - Moses forgot that it is God who supplies the water, as he cried out "Must WE fetch you water out of this rock" Also God had told Moses merely to speak to the rock, but he went ahead and hit it twice.
Numbers 20:14 - The Edomites were desceded from Esau, the twin brother of Jacob, and so kindred to the Israelites. They had settled to the South and East of the Dead Sea. The "King's Highway" was the main trade route running parallel to the Arabah (valley of the Jordan and the Dead Sea), and was the direct route north towards the crossing of the Jordan at Jericho. It should have been open for all travelers to use. The "King's Highway" is still in use today as the main road south from Amman to Petra.
Numbers 21:22 - having skirted Edom, the Israelites asked to travel the next section of the King's Highway, which passes through what is now the Hashemite Kingdom of Jordan
Numbers 24:17 - Balaam's Prophecy of "a Star out of Jacob" is not mentioned again in the Old Testament, but was evidently remembered for over 1,000 years by wise men in the East, for it was the sign of the Star of the King of the Jews that brought the Magi to Jesus at Bethlehem.
Numbers, chapter 32 - the tribes of Gad and Reuben, and half the tribe of Manasseh made a choice based on what appeared superficially to be profitable. In fact, the land east of the Jordan, where these tribes settled, was the most open to attack, and this region was one of the first to be lost to Israel.
Numbers 34:3 - the "Salt Sea" another name for the Dead Sea, with a very high concentration of salts, and the lowest point on the surface of the earth
Numbers 34:7 - the "Great Sea" another name for the Mediterranean
Numbers 34:11 - the "Sea of Chinnereth" another name for Lake Galilee, which is shaped like a Kinnor (old type of harp)
Numbers 35:12 & Deuteronomy 19:1-13 - The "Avenger (or Revenger) of Blood" was a member of the family or tribe of the person who had been killed, and who was appointed to take revenge for the death of a member of his tribe. This could lead to a blood feud, with people killing each other in anger for the death of a member of their family. In a tribal society, there was not much emphasis on fair trial and due process of law with a jury : it was much more like a Wild West lynching party - find the guy and string him up. So people who had killed someone by accident needed a safe place where they could wait until they were given a fair trial.