The blades on many brands of walk-behind mowers rotate to the right, the clockwise direction, when you are mowing. According to some user forums, if the blade cuts clockwise it's a normal thread, counter-clockwise it's left-handed (it's always 'tightening' when cutting).
Mowing the lawn is healthy and can be largely beneficial for your grass. You are trimming the oldest section of grass since it grows from the bottom up.
Cutting higher – typically the top third – shades roots and promotes a root system that is deeper. Deep roots can reach water that is deeper in the soil, giving grass reserve power that enables it to get through dry spells.
Different kinds of grass require different trimming heights. Typically, cool-season grass ought to be trimmed at three and one-half inches. Warm-season grasses should be trimmed at a height of two inches. Check out some lawn mowing tips at Lawndoctor.com.