With the stickers, you – or your participants after enabling the whiteboard – can easily mark something on a slide.
To do this, select the “Sticker” item in the left menu and then select the sticker you want to use from the following submenu. Now click where you want to place it on the whiteboard.
Post-its are used very similarly, except that in the submenu you select whether the Post-it should be attached to the whiteboard anonymously or with the display name.
For Post-its, the selected color is relevant, while stickers are always displayed in red.