Press F10, and small letters appear over each ribbon tab and quick access toolbar item. Alt+H takes you to the Home tab, Alt+N to Insert, and so on. Once in a tab, additional letters appear for ...

But if you press enter in an Excel cell, it will move you to the next cell down rather than inserting a line break.

Microsoft Excel 2013 surrounds the active cell with a dark border to help identify the cell you are editing. Pressing the Enter key after editing the cell moves the active cell to the next cell down.