Hello
They are WTPart BOM usage link attributes. You can edit them in the PSB , in uses tab, or in (M)PSE
Line number is unique under a father. It is commonly used to ordered components in a BOM (mandatory for some ERP if need to interface).
Find Number is not unique under a father. It is commonly used to identify and map parts with a drawing's balloons (for examble an exploded view of an assembly with the related WTpart BOM). Find number is not mapped to CAD system OOTB. Only occurences level by the "reference designator" attribute
In some companies, line or find numbers are used in Change Management to identify a "replacement" for downstream use for example in Service Management or Manufacturing Documentation .
You remove part A and replace at the same BOM level and same line number by part B(ie same function is handle by the new part B)
regards