So the graphical user interface of WordWorth, TurboCalc, etc where all programmed in C?
Most were. In some rare cases assembler or other language were used, but C was the most prominent.
Are there an tutorials of how these where written? such as; how to create a window, a menu, put options in menu, etc?
You can always do all the stuff yourself manually but that is a LOT of work before you even have a menu to work with.
It's much easier and more rewarding to get started with some higher level UI systems such as MUI.