Soft lighting is a light where there is a large gray zone. The gray zone is the spot between light and shadow. Soft lighting is also larger and relatively closer to the object. The details are more highlighted and bright. This lighting is used because it won't cause any shadows on your face. Such as under your nose, eyes or chin. It also does not show the texture of skin so it won't include wrinkles, pimples, etc. You use it by having a larger light source, this will make the light softer . Also when the light is close it seems larger compared to when the light is far away, where it seems smaller. For a single light source you can find a large main light source that is close to you and set up near it. The subject should partly cover it making the light softer or have the light an angle where there are no shadows.