Math-number_help

[Karshi Hasanov]

  Hi,
 I read the User's Guide for equation numbering and labels, but don't
understand how to use.
It does not tell when and where I should do "Insert=> Label...."
I mean after the equation, or before the equation . or anywhere???
Do I have to edit for each equation? Or just one time?
Any way, the instruction wasn't well written for to understand. 
Can any one expalin me it?