This is the 236th most frequent Hindi word.
in
The Hindi word "in" (इन) means "these" in English.
In this sentence, 'पढ़' indicates the action of reading and 'किताब' is the object being read.
मैं किताब पढ़ रहा हूँ।
I am reading a book.
Here, 'में' denotes the location or medium where the action is focused.
उसने पानी में कंकड़ फेंका।
He/She threw a pebble into the water.
In this English translation, 'by my mother' indicates the person responsible for the creation, substituting for an equivalent usage in Hindi.