Okay kiddo, so the United States and Canada have been arguing about the cost of softwood lumber (which is wood used for things like building houses and furniture) for a really long time. The United States thinks that Canada is selling it too cheaply and that's not fair to American lumber businesses. Canada says they're just selling it at a fair price.
So, the two countries made a deal called a "softwood lumber agreement" to try and solve the problem. But, the agreement expired in 2015 and they couldn't agree on a new one. This led to the United States putting tariffs (which are like taxes) on Canadian softwood lumber.
This makes the lumber more expensive for American companies to buy from Canada, which they don't like. And it also means that Canadian lumber companies might sell less lumber to the United States, which they don't like either. So, they're still arguing and trying to work out a new agreement.