Numbers 26 is a census taken of the Israelites after a plague. This verse, Numbers 26:30, is a part of that census, specifically focusing on the tribe of Manasseh and its subdivisions.

Here's a breakdown of what the verse means:

"These are the sons of Gilead:" This introduces a section that lists the descendants (sons, grandsons, etc.) of a man named Gilead. In this context, "sons" should be understood as descendants. Gilead was a prominent figure whose lineage formed a significant portion of the tribe of Manasseh.
"of Iezer, the family of the Iezerites;" This means that one of Gilead's descendants was named Iezer. His direct descendants formed a distinct clan or family group called the "Iezerites."
"of Helek, the family of the Helekites;" Similarly, another descendant of Gilead was named Helek. His descendants formed another distinct clan or family group called the "Helekites."

In essence, the verse identifies two specific clans or family groups within the lineage of Gilead: the Iezerites and the Helekites. These were subgroups within the broader tribe of Manasseh.

Why is this significant?

Organization: The census aimed to organize the Israelites by tribes, clans, and families. This information was important for various purposes, including land allocation, military conscription, and tribal governance.
Identity: These family groups provided a sense of identity and belonging for individuals. Knowing their lineage connected them to a shared history and heritage.
Land Distribution: Later in the biblical narrative (particularly in the book of Joshua), land was allocated based on these family lines. The descendants of Iezer and Helek would have received specific portions of land within the territory allotted to the tribe of Manasseh.
Genealogy: This verse contributes to the overall genealogy of the Israelite people. Understanding these family relationships is crucial for tracing ancestry and understanding the historical context of the biblical narrative.