I want to have a sum formula in a cell such as =SUM(Ex:Ey) while E is the column and x and y are row numbers. Is there a way I can have excel to match x and y to the numbers in other cells? For example: cell D1=3 and D2=12 and there are many numbers in column E. By the end of column E, I want to have a cell that sum only the rows from the numbers of D1 to D2, which is sum of E3 to E12 in this example. The idea is that I can change D1 and D2 to change what rows in column I want to sum.
You can use INDIRECT to reference a range using a constructed string address - SUM(INDIRECT("E"&D1&":E"&D2)).
"E"&D1&":E"&D2 will give you the string "E3:E12" in your example, which INDIRECT will then convert to a reference to that actual range.
Note that INDIRECT comes with a recalculation overhead, but will be fine if you aren't doing too many of them or too complex things!