Yes. You ask a question here, and you get an answer from someone with years of experience, but you don't pay for it. You get something for nothing. This is not a complaint, as it's my choice to give you something for nothing. But you may think about why teachers do this Are we looking for a quid pro quo? Or are we paying it forward? Maybe we believe that what goes round comes round. Or maybe we're just working pro bono publicum. Some people say you can't get something for nothing. There's no such thing as a free lunch. And others don't like to give anything because if you give someone an inch, they take a mile. For example, the guy who sent me a message asking me to correct his homework a few days ago. Unpaid. Grrrr! There you go, some new vocabulary for you! :)

something for nothing = 好吃懒做

Yes, 'something for nothing' is a common idiom that means to get things for free. Similarly, 'something from nothing' is sometimes used to mean to create things, perhaps using magic. Another (somewhat rude) song that uses it is the folk-style song "Something for nothing" by Loudon Wainright.