Referencing Widgets?

[Steve Woodward <stevew goes com>]

I'm sure this is an FAQ but I've been unable to find the right answer.
I'm new to GTK and Linux programming, my background is C programming in
Windows and a little for the Mac. I'm using Glade to build an interface
to a simple one window conversion type app. The confusion I am facing
revolves around referencing widgets. Let's say I want to get the
contents of an entry field. It seems that I cannot reference the entry
field directly as in:

temp = gtk_editable_get_chars(GTK_EDITABLE(entryStartNum), 0, -1);

The above results in a seg fault. I've seen something about
lookup_widget, but you have to specify some other widget as the first
parameter.
So I guess what I am ultimately asking is how to reference
widgets...many thanks in advance.

Steve W