Input file

Hi am new to OrCAD and in learning phase. I am just confuse with the input file creation. My question is that:

1) how to make input file?

    i go through one simple example from book and try to simulate but it won't work. Is it necessary to build a circuit before writing a input file? or it require simultaneously input file and circuit diagram for simulation.

2) How to number the node?

   the input file given in the book is:

 ** DC Circuit Example
  ** Circuit Discription
  VS 1 0 DC 20V
  IS 0 4 DC 50MA
  R1 1 2 500
  R2 2 5 800
  R3 2 3 1 K
  R4 4 0 200
 
  *Analysis Request**
  VX 3 0 DC 0V
  VY 5 4 DC 0V
 
  **Outputs Requests**
  .OP
  .END

and the steps to run the program is :

1) go to start->PSpice

2)File->New->text file

3) type ur input file

4) save input file with .CIR extension

5) from ''Simulation'' menu go to run <input file>

6) the output file will be automatically be given the extension <input file>.out

7) the simulation results file will have the extension <input file>.dat

i complete upto 4th steps but after that  the simulation menu is not available (it is inactive)

iam using OrCAD Capture CIS 16.3 demo

I run some example from book CD with circuit (.DSN extension). It works well and give output waveform perfectly. But there was no input file for the same ckt. So my question is why do we need input file if we can run simulation creating a circuit diagram only?

 Please help me ....iam really stuck with this input file.

Thnx.