Can someone please elaborate on the line item called "Self-Employment
Tax Deduction"?

I am filing Self Employment Tax on Form 1040 Schedule SE, line 5 I
have obtained my "Self-Emloyment Tax". Then in line 6 I am prompted to
calculate "Deduction for one-half of self employment tax" (which is
obviously 50% of my "Self Employment" tax).  I am then prompted to add
this amount to my 1040 in line 30

The question is: what are the principles for "using" this deduction? 
I don't have any income other than my Self Employment Income so what
can I do with this deduction.

This is what the IRS says:
"Self-employment tax deduction.   You can deduct half of your SE tax
in figuring your adjusted gross income. This deduction only affects
your income tax. It does not affect either your net earnings from
self-employment or your SE tax."

But I frankly don't understand. I'd be happy to provide any other
details that may help in reaching an answer.

I understand that any answers provided do not subsititute a tax professional.