Diffusion is when particles move from an area of high concentration to an area of low concentration. Think of it like a little kid party with two bouncy houses. Let's say that both bouncy houses have the same number of kids, but then half of the people in one bouncy house decide to go get lunch. Then one bouncy house is really full and the other almost empty! So you move to the empty bouncy house so you have more space to jump. This is diffusion. So it helps homeostasis because (back to the bouncy house example) you helped even out the two bouncy houses. Now let's say the kids come back from lunch. Now that bouncy house is too crowded so you move back to the now-emptier one. This is diffusion and you would be helping maintain homeostasis, or an equal level, in both bouncy houses.