You can make a simple protective circle just by creating a ring of salt. Obviously you need to visualize, and I personally prefer writing a chant that clearly states the intent. Say the chant as you pour the salt in a ring around yourself or the room or the house, etc.
I agree that there are various solid methods for that. But... there are some types of workings - not beginner workings mind you - that would require some sort of protection like a cast circle. I think that people forget that casting a circle requires a sort of energy work since you won't get your protection simply by cutting your apples and making a circle from them. It's a bit ridiculous if I may state. You may think that it's the circle -- but no, it's your protective energy which helps you with your magical work. Personally I don't do that kind of work any more, so i have little need for complex protective energy circles. I do have elaborate protections up for my personal space and my working space, but they are not Wiccan/Neo-Pagan style cast circles with the Elements/ Quarters/ Watchtowers/ athames, etc.
On a side note, i would also add that the more "experienced" an energyworker you become, you sort of create your own energetic protections without tons of conscious effort. I'm sure others can elaborate more eloquently on this. Now, I haven't practiced circle casting in close to a decade, but I do remember my early efforts in "getting it right." By reading many of the popular how-to books of the time, I was led to beleive that manipulating energy was simple: just point your finger or a wand or a knife, and then viola, a perfect ray of blue energy was emitted, ready for you to shape it at your will. When it didn't *just happen* I would then visualize - and as I'll get into later, just because you visualize energy doesn't necessarily mean it's there, especially for beginners. That basically stated that you simply make a circle and poof, you're protected by some sort of energy... In sum, I found modern occult, especially Neo-Pagan literature to be lacking in good, solid instructional material on energy work basics, most notably how to sense energy.
Although I don't regularly case a circle of protection, it's a nice skill to have when needed - again, all examples of energy work.
Anyway...If you decide to pursue the study of energy work, it is quite possible to develop quite a bit of sensitivity and be able to differentiate types of energy, their sources, and how they move through your body. This is a bit advanced for our purposes, though. The main goal for any beginner student and the focus of these articles is to first sense and feel the energy from our own body. Once success is achieved using these baby steps, it will be a launching pad for further exploration: sensing energy on others, sensing energy from plants and stones, manipulating your own energy and using it for such purposes as creating a protective circle of energy, charging objects, and programming energetic forms.