Whenever people learn I am an English teacher, their first reaction is a bit reserved and hesitant, and their second reaction is usually a grammar question. One of the most common: when is it "who" and when is it "whom." Sadly, most people use whom incorrectly quite often in an ill-fated attempt to sound educated. They will literally use "whom" all the time because they think it sounds smart. It doesn't, however, to the educated people.
And for a bit more information and explanation, I must direct you toward and give a big shout out to the website - www.grammarly.com
Grammarly is an excellent resource for all your grammar questions..