What are tariffs, and why is Donald Trump placing them on Australian exports to the US?

News Snapshot:

Donald Trump loves a one-liner, and saying "tariff" is the "most beautiful word" in the dictionary has become a go-to for the United States' president. He turned to tariffs in his first term, and he says he's using them again in his second to get a better deal from countries the US does business with. Canada was one of Trump's early tariff targets, and tit-for-tat retaliatory measures on both sides have escalated into an all-out trade war, which outgoing Prime Minister Justin Trudeau sees lasting for the "foreseeable future". China, which has also been hit with new tariffs, responded with...