GDB

Dear all,
I am really new in Fortran and GDB.  So sorry if I am asking you some silly questions but I am stuck.

I want to explain to you every steps so there won´t be misleading.
I am running my program in F77 (Path=\F\G77\bin and library   path= \F\g77\lib slatec)
I have also download GNU but I used G77 since I found some practical examples on the net.

I am using the prompt from windows.
I believe that it can be useful a debugger with breakpoints so I can understand
where I am doing mistakes.

I download the GDB version gdb-7.10.1 but unfortunately I cannot understand
how can work. I mean in operative way. I looked at the pdf file gdb.pdf at the paragraph:
Getting In and Out of GDB.

Unfortunately when I am typing gdb at the prompt I got the
Gdb is not recognized as an internal or external command

Do I have to type some path? Which one?
Could you please provide me a practical example?

For instance, I can explain you what I am doing with Fortran in this way there are no doubts or
misleading.


1.       I made a program as the program below:

File panel.for

program panel
implicit none
real tin, Qn, tex
read*, n, e, dt, Tmax

do i = 2, Tmax
    do j = 1, e

      if (j .GT. 1)  then
      tsu =tex(i,j-1)
       end if ...
... end do
end do


2.       I compiled the program in the prompt by typing
C:\F\Panel>f2exe panel
C:\F\Panel> panel

From here my program start correctly by asking me some values.
But when it solves the nested loop I got some odd values  -1IND
A debugger may be useful to understand what is going on.
Best regards,
Christian