Smoothing out skin in an image is actually a fairly simple process and can be done using a few different methods.
One method involves using the "blur" tools in image editing software such as Photoshop. Just select an area of the face you want to smooth out and use the blur tool to make the skin look more even. If you add too much of a blur effect, you can adjust its intensity until you find the right look.
Another technique involves using layers. Firstly, clone the background layer and then brush away any blemishes or skin imperfections with the spot healing brush tool. Next, duplicate the same layer and add some blur to it. Finally, adjust the opacity of the blurred layer so it looks natural and you will have smoothened out the skin with layers!
Yet another option is to use the healing filter, which produces the most natural skin-smoothing effects. You just have to select a small area of the skin and apply the filter until the desired effect is achieved. This can be done a few times with different adjustment options for great results.
No matter which method you choose, the final step should always be to adjust the contrast and brightness of the image to finish the whole look and achieve the desired result.
Hopefully, this answers your question on how to edit a picture to smooth skin. Good luck!