It means the story is not moving clearly from the beginning to the end - either it is out of chronological order, or too many unimportant details are included, or something else is distracting from...
Someone who rambles keeps talking without end. In the process of getting to the point, they constantly repeat themselves. They say essentially the same things, just in different words
The mean distance is the same as the mean of a set of numbers,but this time, instead of them just being numbers, they're lengths. You just simply add up all the numbers and divide the total length,...