The best way to learn English is by reading and trying to understand what is going on in the text study words and their prefixes to know what they mean. If you understand a few words in a text you will gain a better understanding in what the author is trying to say and develop better English skills
Read books, find out the difficult words and find it's meaning. This will enhance your vocabulary. Watch talk shows and speak English with your friends and family members.
I don't have the book so I can't give a line of evidence but Atticus was all about teaching Jem and Scout those little life lessons without them even noticing so this instance was one of those little lessons he gives them. Hope this helps :)
