Hi Rick,
Thank you very much.
Diffusion can be accomplished even with something as simple as a white bed sheet or curtain but most DIY's I've made and those I see used use white nylon ripstop, available from places like Joann Fabrics or other fabric stores. I think it sells for about $7 per yard.
You can hang the material about 2 feet in front of the flash head or create a frame using 1/2" or 3/4" PVC tube. Simple and inexpensive and works great. No, it's not the same as using a lightbox but it gets the job done.
When I was first learning about light and lighting I made very simple frames with white diffusion and then advanced to more complex frames that added black panels on the sides to contain more of the light. I've even DIY'ed a huge lightbox with a grid, as seen below.
The most important part in all of this is to diffuse (scatter) the light and have the light source about as far from the subject as the size of the longest dimension on the front face of the panel or material. If we use a 36" square softbox as an example, the optimal distance from the subject is about 1 to 1.5 times the length of the longer edge, and in this case, it's square, which means that you want the front face of the softbox anywhere between about 36" to 54" from the subject.
The concept is to increase the relative size of the light source, thus softening shadow edges and transitions from shadow to diffuse value and from diffuse value to highlight. The larger the light source relative to the subject, the softer the light. This does lower contrast but in a very pleasing way and when it comes to photographing people, in most cases, soft light is pleasing and desirable.
Hope that helps. Any other questions, feel free to ask.