Using a soft background is a very effective technique to bring the main subject into prominence. In fact it is so widely used many lenses are designed and sold specifically for this task.
But you do not need a specialty lens to induce this.
This weeks exercise takes us back to the depth of field exercises we did a few weeks ago. The bottom line being that:
Using a telephoto or long lens means small depth of field. The longer the lens the easier it is to induce this look.
Having the subject very closet to the lens with the background further away also helps to induce softer backgrounds.
The shapes and composition of the negative space needs to support the main subject of your photograph.
Use a smallest aperture number, where you use your lens wide open.
You should be able to do this exercise with a standard lens, or even a short telephoto lens. You can even do it with a moderate wide angle, but not with an extreme wide angle.
This weeks exercise is simple. Photograph objects, interesting subjects and work the out of focus backgrounds by utilising short subject / lens distances and longer background / lens distances. See my examples bellow. Post multiple examples of well composed photographs where the subject is isolated from a well composed background.
Aperture numbers confusing? They are actually fractions just like shutter speeds. F 5.6 is really 1/5.6 just like 1000 = 1/1000. Hence when people refer to small they really mean large. It doesn’t really matter, all you need to remember is what they do.