— Looks like that's the major factor of a function..
Big o notation expresses the maximum time something takes and how it depends on the thing's structure
— Say you have a data structure, appending takes O(1) time and getting an element takes O(log n). This means that the time to append is consant: if the structure has 0, 1 or 100 elements it's the same. Getting an element doesn't always take a number exactly log n (n is the length of the struct), only the longest amount it can take is log n