Use of bottom up heap construction for sorting

[MyraParks]

Given the word “banana” and you are supposed to use the bottom up heap construction to do the sorting, the child in every sorting will be smaller than the parent but am wondering how to do a comparison between ex a & n given that n is bigger than a. Why is a bigger than n? https://www.theengineeringprojects.com/2019/11/introduction-to-inheritance-in-c-sharp.html