Reading this entry in the Tcl/Tk online reference i came across this paragraph where it states:
The combobox widget also supports the following ttk::entry widget subcommands (see ttk::entry(n) for details):
- bbox
- delete
- icursor
- index
- insert
- selection
- xview
I know in this case of the Combobox widget it's comprised partially of an Entry widget but how exactly are subcommands used?
This is the common Tk command structure, and you'll need it to interact with any Tk widget. A subcommand of a widget is done by using the pathname of the object as the base command, then the subcommand you want. E.g.,
ttk::combobox .cb
.cb insert 0 "my text"