Sound will not play through speakers

John Dimick probably has the correct answer.  Just to add that even if the setting look correct, sometimes it help to open the menu, reselect your Macbook's built in sound card, then Apply it again.  This can happen if some other app on your computer has grabbed the sound card and not released it properly.

If the above doesn't work, the other thing to try (if you're in Multitrack view) is that the output for your track(s) (in the Settings box at the left end of each track--a drop down menu marked with a left-facing arrow) is set to "Master" and, on the Mixer View, that the faders for your track(s) and the Master are both turned up.

Finally, and pretty unlikely, make sure the little box with the "I" in the same settings box isn't ticked--this changes the feed from that track to the input rather than playback.