creating the – symbol

After reading websites and documents I noticed that the symbol –  is used 
often.  In some cases the symbol m- is used.  What I hav noticed is that when 
using the n- (or m-) symbol it is as one character.  Does anyone know how to 
create the symbol?  I already went into insert 4 and it is not available there. 
 Thanks in advance for any help, Judith

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