Oh goodness guys! You need some proper Garageband education!
That is my editing software, and as I don't use MIDIs I HAVE to compose manually! Here's how!
There are certain loop tracks that are colored green. These are the loop tracks in which notes can be edited. Simply double click on the green bar(s) of music which you want to edit. Also, by selecting a green bar, you can then click on the scissor button at the bottom left hand edge of the Garageband window.
If notation has not previously been used within this file, then the first thing to pop up will be an editor based on a piano scale, called piano roll. From here, you should select the tab to the right of the selected "piano roll" tab called "Score" and containing a ô next to it. This will get you to the sheet music section. If you don't read music, you may use the piano roll by plugging in notes and click-dragging them to increase/decrease values (I don't use this as it is not my kinda thing, and can be less accurate at times)
Once you click the "Score ô" button, you should see a blank sheet of music; if untampered with there should be whole rests in each measure. You should see a grand staff (treble and bass clef) as well as a tab at the top with measure numbers. Now here comes the important stuff:
-To create a note, hold down the control key while the mouse is over the staff. A faded, grey-black note should appear; continue to hold down Ctrl while moving the mouse up or down the staff to place where you want the note to go. Sharps and flats will play into this as well; as you move along you will see these appear. You can place the note in near any audible octave, and can pick any of the 12 chromatic notes.
-To extend the length of a note: There are a few ways of doing this. First off, before you create a note, you should notice the tab on the left within the "Score" box which states a note value (ie Whole Note) and shows the note. This will be the value of the note created. To change the value, simply click the tab and select the musical note which corresponds with the value you want. Many various values are available: the notes can be as fast as 32nd notes, and have the ability to be triplets, pedal tones, quavers, etc.
The second way to change a note's value is after it is created. Click on the note on the staff, and it should now be highlighted. You should see a green tab on the note, varying in length depending on the note value. To change the value of the note, simply click/drag the (right) end of the green tab, and move it left or right to increase/decrease note values. With an infinate loop bar, this note has the possibility of being held for as long as you desire. You may shorten or elongate it from whole to 32nd.
-Copy/paste and Creating measures: Continue adding notes to the measure until you have satisfied the note values you have wanted to place. Keep in mind, you are under the constraints of the time signature you are in; be careful not to oversustain notes (this will be included in the next section) Also, just as you can do with loops on the main screen, you are able to copy/paste notes and place them virtually where ever. Simply highlight/select the note(s) you want to change (using the click/drag "lasso" highlight method that you may use when copy/pasting text on a document)
Release the mouse and press/hold the option key. Then click/hold a highlighted note and it should replicate itself as you move it from left to right. This enables you to easily repeat phrases in your music, and use those notations/compose easily
-Time/Key/Contraints:
>Time: The time signature which you have selected for your project directly affects your measures/composition. While there is no limit on the amount of notes within a bar, there IS a limit on how many spaces can be filled (up to the subdivision of 32nd) This means that while you can place notes where ever, spots for rhythm will fill up, and thus your measure will become one big mess of noise. Fix this by adjusting how long the notes are held, and by adjusting how many notes are in the bar until a rhythmic figure is created which you like.
>Key: Key doesn't really limit your composition; just keep in mind that if you have a composition in the key of...let's say Db, certain notes that would be flat in concert C would show up as naturals here (vice versa as well)
-----To change Key and Time, go to the "Project label: on the blue digital screen (click on the icon within that blue-ish box and select the metronome) You can change the time signature of the piece, the key of the piece, as well as the quality (major or minor)-----
>Constraints: -You can only copy/paste for the length of the green project measures/bars. Once the amount of measures is used up (ie 4 measures) you can't copy/paste notes into a different green project bar.
-***see time above***
Filled in?! Let me know if you have more questions!