There are many different blur options in Photoshop. My most common use for a blur filter is to soften a background or to change the focal point. I typically use Gaussian Blur for these kinds of things. Surface Blur is another useful filter when trying to soften skin. Luckily most of the blur filters work the same.
1. First open your image in Photoshop. Again, this is a destructive filter, so I would recommend duplicating it before moving on.
2. Next go to Filter > Blur and select what type of blur you would like. In this case I’ll use Gaussian since that is the one I use the most.
3. Next adjust the amount of blur to your liking. I honestly think it’s just easier to slide the bar back and forth until it visually looks good. I almost never pay attention to the number.
4. Here is the final result. Usually you need to apply a mask or erase parts of it so some parts are in focus and some are blurred.