The Composer window has three views which can be changed from the drop-down menu on the upper left. Select "Piano Roll." The Piano Roll screen has a piano keyboard on the left, and grid lines on the right. If you click your mouse on the keys, you can hear the corresponding notes. You can specify the range of notes available by clicking the "Add Sounds" button just below the keyboard.

Click Add Sounds. You will see a menu from which to select the range of notes available. For Lowest Note, select G-4, and range of notes, 15. Press OK. Now, by clicking on the piano keys, see if you can pick out the tune to Frere Jacques, starting on the 'C' note. You will notice that the notes pretty much follow the 'C major' scale. If you are unfamiliar with scales, click here. To actually enter the notes, use your mouse to click on the grid on the same line as the note you want to enter. The bold lines in the grid represent measures, and the lighter lines divide the measure into 1/4 and 1/16 intervals. You can change this from a dropdown menu just above the grid, but let's stick to the default setting.

There are two ways to specify the time value of a note: either from the dropdown menu marked "Note:" or by entering a note, then dragging the mouse over it. If you are unfamiliar with time values, click here. Using 1/4 notes, enter the notes for the first two measures. Your screen should look like this: