I will try to answer, without reference to low-level programming (or any programming language), without mention of history, or much maths.
As already stated in some answers, we do not count from zero (using the value 0 to represent 1, and 1 to represent 2 (Usually)). So what do we do?
We measure from zero. If I give you a ruler, and ask you to measure something, you measure from zero. If I ask you to tell me how far a cell in an array is from the start, then you measure from zero (the first cell is zero from the start: it is at the start), the 2nd cell is 1 from the start.