Mounted on the hook with the bobbin rotated in a clockwise direction, it will open up the strands of fibre, allowing it to lay flat on the hookshank. If the bobbin is rotated in the opposite direction this will tighten the fibres, which now take on a round profile. Danvilles also manufacture threads that will lay very flat indeed. Monocord, or a very good, flat thread by Thompsons, called Monobond, both have their devotees. I highly recommend it.
Threads HERE is a resume of some good tying threads.
I am biased towards the US products, simply because I have used them for so long. This will certainly put you on the right track to start learning about thread control, as this will be the thread I will use for my instructions on tying procedures. The first stage to tying a fly is to mount the hook in the vice with, I hasten to add, the point and barb exposed from the vice jaws. The worry that I will catch the thread on the hook point is irrelevant - if I have proper thread control. You will very soon learn to avoid that pitfall.