The Speech Bubble Tool allows you to create speech bubbles with several different callout options (the thing that points towards the speaker). The stroke width specifies the thickness of the bubble's border in pixels.
The Callout Position option determines which side of the bubble the callout drops down from (left or right). The Callout Direction option indicates which direction the callout is facing (regardless of its position).
When you complete drawing your Speech Bubble, it will be created as a Pen Element. This gives you the freedom to adjust it further if you desire (by manipulating the resulting bezier points, for example). It is also selected automatically so you can fine tunes its position.