VLOOKUP searches for a value in the leftmost column of a range and returns a corresponding value from a specified column to the right -- for example, =VLOOKUP(A2, ProductTable, 3, FALSE) looks up the value in A2 within ProductTable and returns the matching value from the third column, with FALSE requesting an exact match. A key limitation is that VLOOKUP can only look to the right of its search column; INDEX/MATCH, a combination of two functions, searches in any direction and is generally considered more flexible and resilient to inserted columns, though it has a steeper learning curve. The most common lookup error, #N/A, usually means the lookup value doesn't exactly match anything in the source range -- often because of extra spaces, mismatched data types, or a typo, which is why cleaning data first matters so much.