Some ideas are larger than others, and you can make that apparent by resizing your sticky notes.
To resize a sticky note:
Click to select a sticky note.
Hover your cursor over any corner of the sticky note.
Click and drag the resize box to change the size.
Or, you can choose Default size, Resize to biggest, or Resize to smallest from the toolbar.
You can also select multiple objects with Shift + click + drag. Then, click and drag the resize box from one of the corners of the selection.