Tapping the Pen/Paper icon will display your annotating tools.
Annotation options will appear top left of your screen, giving you a range of different features.
The Pen tool will give you the ability to write freehand notes with your finger or a stylus. Once a note is made, you can select and configure the note e.g. colour, thickness etc. located top right and below.
The Highlight tool has several options available underneath it. These are accessed via a 'long press' - highlight, strikethrough and two styles of underlining.
These annotations are also editable in terms of colour etc..
The Note tool allows you to add sticky note comments and also has other tools available underneath it, accessed via a 'long press'.
The eraser will give you the flexibility to erase any freehand generated annotations.