By default, the Shapes toolbar contains tools to create various shape markups.
If the toolbar is currently hidden, go to View > 
Toolbars and select it to show it.
Line (L): Adds a line markup.
Arrow (A): Adds an arrow markup.
Callout (Q): Adds a text callout markup.
Rectangle (R): Adds a rectangular markup.
Ellipse (E): Adds an elliptical markup.
Polygon (SHIFT+P): Adds a polygon markup with no set angles.
Cloud+ (K): Adds a polygon markup with a cloud-like appearance and callout box preset.
Image (I): Inserts an image from a graphic file accessible on your workstation.
Crop Image: Crops an image markup.