Loop Command in Power Query

aditya 

As variant, to receive such result

and ignoring column Value in source data, not sure for what it is needed, we may generate list from start to end for each record, group table on Item and Side, as aggregation union lists for the groups and count them. Entire script is

let
    Source = Excel.CurrentWorkbook(){[Name="Table1"]}[Content],
    #"Add column with lists of points" = Table.AddColumn(
        Source,
        "List values",
        each {[Start]+1..[End]}
    ),
    #"Groupe by Items and Sides and count union" = Table.Group(
        #"Add column with lists of points",
        {"Item", "Side"},
        {
            {"Count",
             each List.Count(List.Union([List values]))
            }
        }
    )
in
    #"Groupe by Items and Sides and count union"