...
Click on "Add new" in the navigation. This will place a new sticky note in the center of the screen. Be aware that if you click on the "Add new" button multiple times consecutively the new sticky notes will stack on top of each other.
From a sticky palette in the navigation
Press shift+right-click on the "Add New" icon in the menu to display the palette. You can then drag and drop new stickies from the palette. You can close the palette by pressing shift+right-click again.
Clicking and holding
...