First, select in the toolbar the type of annotation you want to insert and then place it at the desired position in the document.
There are several variants of the annotation types for highlighting text and drawing shapes. (You can recognize this by the small arrow in the corner of the button.) If you press such a button a little longer, a menu will open to select the desired variant.
Below you will find an overview of all possible annotation types.
On the buttons and menus in the image below, you will see a number. The corresponding annotations are marked with the same number.