This verse, 1 Chronicles 1:20, is a genealogy, specifically a part of the genealogy of Shem, one of Noah's sons. In this context, "Joktan became the father of..." means that Joktan was the ancestor of these individuals.

Here's a breakdown of what it implies:

Joktan: Joktan is a figure in the Table of Nations (Genesis 10) who is identified as a son of Eber (Heber). He is considered the ancestor of various Arabian tribes.
"Became the father of": This is a common phrase in genealogies. It doesn't necessarily mean direct fatherhood in the modern sense. It could refer to a line of descent, with Joktan being the founder or progenitor of the groups or tribes represented by these names.
Almodad, Sheleph, Hazarmaveth, Jerah: These are names of individuals or, more likely, groups or tribes who were descendants of Joktan. They are generally considered to be associated with South Arabia, based on geographical and historical connections of similar-sounding names.
Genealogical Significance: Genealogies in the Bible, especially in Chronicles, served various purposes:

Establishing Identity and Lineage: They demonstrated a person's or group's place within the larger Israelite or, in this case, global framework.
Connecting to Ancestral Land and Blessings: They could tie a group to promises made to their ancestors.
Illustrating God's Plan: Genealogies highlighted God's role in history and his covenantal relationship with humanity.

In summary: The verse indicates that Almodad, Sheleph, Hazarmaveth, and Jerah were descendants of Joktan, and that Joktan was thus the ancestor of the tribes or groups associated with their names. This placement suggests that these groups were considered to be related to the Semitic line and, specifically, to the peoples of South Arabia. It's important to remember that biblical genealogies are often more symbolic and representational than strict biological accounts.