Without any equations, the diffraction may be considered a fixed blur that degrades focus across the image and into the scene. The only camera variable that impacts diffraction is the aperture. The smaller the aperture, the more diffraction blur will occur.
Graphically it looks like this:
Illustratively the total blur curve looks like this, showing that even at the point of focus there is a degradation in focus because of diffraction:
Bottom line: The last two posts have discussed the two contributions to depth of field and achieving tact sharp images. The focus bar manages both diffraction and defocus, and allows you to find the optimum focus.