What is the correct way to put a helmet on?
The manual pretty much sums it up. The helmet should sit naturally at the correct place without the straps. The straps are only there to hold it in place in a prang, when a bit of chaffing / bruising  is the least of your problems.  A small amount of slack (you should be able to fit two - three fingers between the strap and you) is best. If the straps are pulling the helmet out of position, loosen them.  

Be aware that not all of us have the same sized and shaped heads, so it is possible your helmet is just not a good fit.

Note also the bike helmet only protects against brain injury. Theres plenty of scope for a large amount of pain and cosmetic damage - think what a face plant at 30mph would do, and still scope for massive brain injury with a properly fitting helmet. 

Its a reasonable argument that wearing a helmet provide a false sense of security - essentially if you would not do it without a helmet, don't do it.  

Your helmet is a very last resort -  a "get out of jail" card that only works sometimes. Worth wearing? - I have a mate with a brain injury (non cycling) ... need I say more.....