An attribution model distributes the credit for a conversion among the touchpoints of the journey: last click (100% to the last), first click (100% to the first), linear (equal shares), U-shaped (40% to the first, 40% to the last, 20% in the middle). Whatever the model, the sum of credits equals the total value of the conversions.
Example
Journey: email, search, direct. Linear: 1/3 of the conversion to each.