There are 12 nonsense words and 12 bolded letters.

The position of each bolded letter will tell you whether it goes at the beginning, end, or in the middle of the word.

H is in the middle position, so adding it somewhere in the middle of the word TIS creates the word THIS

(middle) H = Tis = This
(lower) S = I = is
(upper) T = He = the
(upper) W = arm = warm
(lower) D = be = bed
(upper) T = hat = that
(upper) B = utter = butter
(middle) R = coves = covers
(upper) E = every
(middle) W = Dan = dawn
(upper) W = heat = wheat
(upper) P = lease = please

This is the warm bed that butter covers every dawn. Wheat, please.

Something warm that you put butter on? Wheat is a variety of it? Gotta be TOAST.