When it comes to artificial lighting, your choice of modifier is one of the most fundamental and crucial creative and technical decisions in the entire process. If you are new to working with artificial lights, this excellent video tutorial will give you the sort of practical knowledge you need to know which modifier is right for each photo you wish to make, along with a variety of illustrative examples.
Coming to you from our good friend, Pye Jirsa, with Adorama TV, this awesome video tutorial will show you the fundamental properties of lighting modifiers and how they affect your images. Of these, probably the most fundamental is soft versus hard light. One mistake beginners frequently make is confusing absolute size with relative size. The size that matters is the size of your modifier relative to the subject (this is why the sun, despite being huge, produces hard light, since it is so far away). Thus, a small modifier can make soft light and a large modifier can make hard light, all by varying their distance to the subject. Check out the video above for the full rundown from Jirsa.
If you want to continue learning about lighting, be sure to check out "Illuminating The Face: Lighting for Headshots and Portraits With Peter Hurley!"