Ah!

You need to use layers. Typically, you'll work primarily on layer 4. To put the red bricks "behind" layer 4, you can put them on any layer behind that, but people typically use layer 5 for that. Press ctrl+5 to open up the layer 5 properties; make sure it has the same width and height as layer 4. Then set X- and Y-speed to 1, and both auto speeds to 0. Now you can simply put the red bricks on layer 4, behind the objects you want it to be covered with.