English prepositions - in and at, at or in the beginning, in or at the end

Engish prepositions can be a pain in the ass, sorry for my choice of words, but this is the closest deffinition possible! :) Let's study 'IN' and 'AT' in the phrases 'in/at the end' and 'in/at the beginning'.
p.s. I am on vacation now in Germany. But I will try to post videos as often as possible!