Algebra tiles stand for parts of an expression. A small square is 1, a long rectangle is x, and the big square is x². The red tiles are the negatives.

In the tray, matching tiles are like terms, so they combine: three x-tiles read as 3x. In the area layout the tiles fill a rectangle, and the rectangle's area is the product. Three rows of (x + 2) cover 3x + 6, which is the distributive property you can see.