Stock Cover Calculation

Someone previously provided the following DAX solution to calculate Stock Days cover:

Can someone please explain to me how to get this to work?

Column = 
VAR s = Table1[Stock]
VAR w = Table1[Week]
VAR x = Table1[Product]
VAR t =
    FILTER ( Table1, Table1[Week] > w && Table1[Product] = x)
VAR t2 =
    ADDCOLUMNS (
        t,
        "total", SUMX (
            FILTER ( t, Table1[Week] <= EARLIER ( Table1[Week] )&&Table1[Product]=EARLIER(Table1[Product])),
            Table1[Sales Plan]
        )
    )
RETURN
    IF (
        COUNTROWS ( FILTER ( t2, [total] >= s ) )
            > 0,
        COUNTROWS ( FILTER ( t2, [total] < s ) )
            + DIVIDE (
                s
                    - MAXX ( TOPN ( 1, FILTER ( t2, [total] < s ), Table1[Week], DESC ), [total] ),
                MAXX (
                    TOPN ( 1, FILTER ( t2, [total] >= s ), Table1[Week], ASC ),
                    Table1[Sales Plan]
                )
            )
    )