The Trill ornament is quick multiple repetitions of two notes: the neighbor note and the main one. These notes lie one or two semitones, one whole tone, apart. Sometimes a trill starts with a dissonant tone above the main.
The Prall ornament represents an alteration between two notes. The neighbor lies one or two semitones above the main one. This ornament ends with the concluding return to the main note. There are a lot of variations of the Prall: Prall Prall, Up Prall, Down Prall, Prall Up, Prall Down.
The Mordent ornament differs from the Prall in that the neighbor note lies one or two semitones below the main one. The alteration ends with the concluding return to the main. There are several types of the Mordent: Prall Mordent, Up Mordent, Down Mordent.