Navigate to the handbook page for MuseScore 3: Tremolo
Tremolo is the rapid repetition of one note, or a rapid alternation between two notes or chords. It is indicated by strokes through the stems of the notes or chords. If the tremolo is between two, the bars are drawn between them. Tremolo symbols are also used to notate drum rolls.
To add tremolo to a single note, select the note head and double-click the desired symbol in the tremolo palette.
In a two note tremolo, every note has the value of the whole tremolo duration. To enter a tremolo with the duration of a half note (minim), enter two normal quarter notes (crotchets), and after applying a tremolo symbol to the first note, the note values automatically double to half notes.