Embellishments are extra notes that add a bit of spice to a melody. Embellishments can be used in music in several ways.
Bars from left to right:
not notated at all...
Embellishments are entirely left to the performer. Depending on the music style a performer may add all kind of embellishment like vibrato, trills, grace notes, glissandi etc.
Implicitly notated embellishment often uses ornamentation signs like prall-trills, mordents and the like. The exact interpretation is left to the performer who should know whether trills are meant to be played fast or slow, before or within the main note's duration, using chromatic or diatonic notes etc.
Optional embellishments (like ossia) provide a play-suggestion/prescription/alternative.
Explicitly notated in-line embellishments may clutter the melody seriously, making it difficult to grasp the main notes from the melody.
Use the playback-dialog to define the desired style of playing embellishments
See also: trill-menu