Help deciphering formula

the 0 is to specify an exact match for the MATCH function
The -2 is used to reduce the row number by 2 rows
The +10 is used to add 10 columns to the $U$15 column
The 4 is to say that this address is a RELATIVE one.

In this formula: =IFERROR(IF(S42="","",INDIRECT(ADDRESS(MATCH("Jars",$U$15:$U$35,0)+ROW($U$15)-2,COLUMN($U$15)+10,4))*AE11),"")

The MATCH function requires 3 parameters:
- the item to find
- the range to search
- the kind of match
...0=Exact match (but, not case-sensitive)
...1=Approximate match (items must be sorted)
...-1=Reverse order match (items must be sorted)

This section: MATCH("Jars",$U$15:$U$35,0)+ROW($U$15)-2
determines which row on the worksheet to reference

If the matched item is in U16...
This part: MATCH("Jars",$U$15:$U$35,0) will return 2...the second item in the referenced range.

It appears that we want to get the item that is one row ABOVE that matched item's row.
Consequently, to get the actual row of that item we need to add the beginning row of the referenced range (in case it changes) and subtract 2
=2+15-2
=15

This section: COLUMN($U$15)+10
returns the col to be referenced, which, in this case, is 10 columns to the right of Col_U.
=21+10
=31

I hope that helps.