To create a RichEdit component you need to right click on layout window, select "User Class", then in the pane to the left of the layout window you need to type RichEdit (there's a drop down button but RichEdit isn't in the list yet) - you can also put RichEditWithToolBar - this is the "class name field" and to its right is the variable name field (where you put the name you choose for the RichEdit object).
You also need to add this to your header file before the .lay include
#include <RichEdit/RichEdit.h>
and you need to add the RichEdit package to your main package.
(RichEdit is a bit more complex than most widgets - it's also powerful).