Notes can be entered in the Score Editor or the Piano Roll Editor using the mouse. Make sure the note object is selected in the object palette. Select the pencil tool (second from the left in the toolbar) and click where you want to put in the note. The note is drawn with the duration equal to the duration value you have set in the durations palette in the main control area. You can change this any time you want by clicking on a new note value in the durations palette. Be aware that the note you enter doesn't get put in until you release the mouse button. You can see exactly where the note will go before you release the button.
As you move the mouse left and right before releasing the left mouse button, the note being entered moves forward or backwards in time along with the mouse. The amount of time between positions is equal to the step value. The position in time where the note will be entered is shown in the mouse time locator.
In the Score Editor, as you move the mouse up and down before releasing the left mouse button, the note being entered changes pitch with the mouse and as it does so, it stays in key. This is usually what you want, but sometimes you will want to enter a note with a pitch that is not in the key signature. You can move a note chromatically by using the arrow keys before releasing the left mouse button. For example, to enter a C sharp in the key of C, move the mouse so that the note appears as a C natural. Then, before releasing the left mouse button, press the UP ARROW key once. Now release the left mouse button.
Notes are entered with the voice set in the voice palette.