Grabbing a cell by position with INDEX
=INDEX(reference, [row], [column])
INDEX returns the value at a given row and column inside a range. Positions are relative to the range, not the sheet: row 1 is the first row of the range, wherever it sits.
=INDEX(B2:B11, 4)returns the 4th item in a single column.=INDEX(B2:E7, 3, 2)returns row 3, column 2 of a table.
On its own INDEX looks a bit pointless (why not just type B5?). It becomes powerful when the position is calculated, usually by MATCH. That's the classic INDEX MATCH combo.