I am ... new to both Linux and gFortran.
I tried typing the name of the executable and giving a carriage return: got the response command not found.
The most probable cause of this is that the subdirectory where you created the executable is not in your PATH.
You should use the command:
(where <CR> is your carriage-return, Enter key, whatever.) The "." represents the current directory. Without the "./" prefix to tell the shell that the command that follows may be found in the current directory, the shell will look at the (colon-delimited) list of directories contained in the shell variable "PATH". Issue the command "echo $PATH" to see that list.
As for the compiler's debugging options, I can't help you there; I haven't written any new FORTRAN code in over a decade and none under Linux. I would hope
that the debugging code would be nice enough to point back to a line of the FORTRAN source code when things go south at runtime. Otherwise, it'd seem pretty useless. But that's just a guess. Have you read the manpage for the compiler?