"When Pharaoh [see also Who Was The Exodus Pharaoh?] heard of it, he sought to kill Moses. But Moses fled from Pharaoh, and stayed in the land of Midian; and he sat down by a well. Now the priest of Midian had seven daughters; and they came and drew water, and filled the troughs to water their father's flock." (Exodus 2:15-16 RSV)
And so it was that Moses found himself out in the desert wilderness of the Sinai (see The Sinai Peninsula and Bible Places), the first time, long prior to the Exodus, and how he came to meet Reuel, or Jethro, a priest of Midian, who would soon become Moses' father-in-law.
Jethro was also called Reuel. Reuel meant friend of God, while Jethro meant excellence. Reuel was apparently his personal name, while Jethro may have been a more official or honorary name.
The Midianites originated from Midian, a son of Abraham (Genesis 25:1-2), which therefore actually made Jethro and Moses distant cousins. The Midianite territory consisted mostly in the area east of The Dead Sea and The Jordan River, but during the time of Moses also included a large part of the Sinai.
Moses married Zipporah, one of Jethro's seven daughters. Together during their life in the Sinai they had two sons - Gershom and Eliezer (Exodus 18:3-4). When God sent Moses back to Egypt for the Exodus, Zipporah and their two sons remained safely with Jethro until after Moses returned to the Sinai with the Israelites.
Jethro unknowingly (or possibly knowingly) played an important part in preparing Moses for his Exodus mission. Moses had been born and raised in Egypt. He had lived a relatively easy life - the hardships of living in the Sinai wilderness would have been unknown to him while growing up in the home of the Pharoah's daughter. (Exodus 2:10)
During the long time that Moses lived and worked keeping Jethro's flocks, Jethro no doubt taught him all about desert life. Many are surprised when they first read that Moses spent 40 years out in the desert wilderness before returning to Egypt for the Exodus. Certainly by then he would have become well familiar and accustomed to life in the Sinai, where he would later spend another 40 years leading the Israelites during their Wilderness Journey before their entry into the Promised Land. The long time spent out in the very same wilderness where the freed Israelites would be taken and held for 4 more decades was all part of God's education of Moses. And that training was accomplished through Jethro the Midianite.
Fact Finder: What is the name of the mountain where Moses saw the famous
burning bush while tending Jethro's flocks?
(a) Hermon (b) Horeb (c) Moab (d) Carmel