English is well-known for being a very idiomatic language with lots of old expressions and new ones being born all the time.
Let’s take two quick examples and at the bottom we’ll provide links to some good sites.
Cash cow: A cash cow is a product which has a low investment cost for the company but easily brings in a lot of money. Sometimes people say slot machines at casinos are a type of cash cow.
Go back to square one: This is an expression which means to start over from the beginning. Example: After weeks of negotiations everything fell apart and we couldn’t come to an agreement. We’ll just have to go back to square one.
There are many business idiom sites out there. All of these looked good to us:
http://www.idiomconnection.com/business.html (has free quizzes too)
Sometimes someone wants to show off a certain new skill or joke. But what if that skill is not very impressive, or the joke is not very good? Or what if it is a little impressive, but not enough for that person to really boast about? We might say to that person: “Well, don’t give up your day job.” It means, whatever you just said or did, it wasn’t good enough to be a professional!
It may sound like it is a rude comment, but actually most Americans just think it’s a slightly funny comment.
In the case of this cartoon, this spider’s joke isn’t funny enough to make the man laugh. He even says, “Don’t quit your day job.” It means, just keep being a spider. Don’t try to be a comedian because you’re not that funny!!
Learn That Word: Learn vocabulary and spelling on this site. You can narrow down your lessons by commonly misspelled words or TOEFL vocabulary.
BBC Learning English: This resource from the British channel offers all kinds of lessons and tips for learning English, including pronunciation, vocab, and grammar lessons.
Learn English Kids, British Council Though this site is aimed at kiddos, anyone trying to get a grasp on English spelling and speaking will find its games fun and useful.