In or at the beginning?

English as a Second Language English Vocabulary, Grammar and Idioms
1

What’s the difference between “in the beginning” and “at the beginning”?

Thanks

2

Read the discussion here, where you will also find links to further explanations:
english-test.net/forum/ftopic26894.html

The Oxford Learner’s Dictionary:
At the beginning (of) is used for the time and place when something begins. In the beginning (= at first) suggests a contrast with a later situation