What’s the deal with Tariffs starting tomorrow?

So what’s the deal? Everything that crosses the border tomorrow from Mexico is going to have a 25% charge on it paid by the importer? Can they enact it that quickly, no set up required? So a box of bell peppers that got bought for $10 will now cost the importer $12.50? Surely that will get passed on to us consumers, no?

https://www.reuters.com/world/americas/north-america-braces-new-trump-tariffs-saturday-deadline-nears-2025-01-31/