You can add lettering to a Chenille design by typing it directly in the design window, or entering it in the Object Properties - Lettering dialog.
By default, chenille lettering objects are filled with either Coil or Perpendicular Fill stitch depending on how they were created. See ES Chenille fill stitches for details. You can also apply other fill stitch types, such as Straight or Island Coil, as with other embroidery objects.
The fill stitch type cannot be changed when the letters are used in a design, as Straight and Coil require different filling techniques. For example, if an alphabet was digitized with Straight, the shapes are probably filled with two perpendicular layers, which cannot be stitched with Coil.
Chenille alphabets use either As Digitized, Closest Join or Bottom Join method. See the lettering chapters in your Wilcom ES User Manual. When digitizing a Chenille alphabet, you can insert Needle Height. All letters in the alphabet must have the same number (or a multiple) of needle height changes. See Setting the offset needle height for details.