To find the smallest element, assume the first element is minimum. Store arr[0] in min. Then loop through remaining elements, comparing each to your current minimum. When you find an element smaller than min, update it.
After checking all elements, min holds the smallest value. You've compared every element against the current best candidate. Why start with arr[0]? Using an actual element guarantees your result is real data.
If you started with a huge number and the array was empty, you'd return meaningless output.