Processing arrays with for loops follows a template you'll use repeatedly. Declare index i, start at 0, loop while i < size, increment i, access arr[i] inside. This becomes second nature.
Nearly every array algorithm uses this structure. Finding minimum? Loop and compare. Counting matches? Loop and check condition. Summing values? Loop and add to total. The pattern is so common that modern C++ added range-based for loops.
But understanding index-based loops matters because existing code uses them, and sometimes you need the index.