No symbol table is loaded. Use the "file" command. --- new to gdb: please help !

[Grazia Russo-Lassner]

hello,

I am trying to debug a program, but when I enter a breakpoint I get
No symbol table is loaded.  Use the "file" command.

This is what I do:
gdb filename-of-executable
break 48	#to break at line 48

then I get:
No symbol table is loaded.  Use the "file" command.

Could someone help ?

Thank you in advance.

Grazia