Where can I buy Fortnite bricks?

Excuse me, I'm curious about where I might be able to purchase Fortnite bricks. I understand that Fortnite is a popular video game, but I'm not familiar with the concept of bricks in this context. Are these digital items or physical objects? And if they are digital, which platforms or marketplaces offer them for sale? I'd appreciate any information you could provide to help me understand how to acquire Fortnite bricks.