The Buffer Tool is accessable in the Shapes Tab in the Vector Tools Panel in the Side Panel. It can be used to create a buffer polygon of a specified size (in km) around selected features in the Shapes Layer.
Before using the Buffer Tool, there must already be at least one feature in the Shapes Layer on which to base the buffer polygon. Features can be created using the Draw Tool, or added from other vector layers loaded onto the map.
To use the Buffer Tool, follow these steps:
Make sure that Shapes is selected in the Active Layer Selector in the Control Panel.
Select the features on which you would like to create the buffer in the Shapes Layer.
Enter the width the buffer should be (in km) in the box in the Buffer Tool: km
Click the Buffer button in the Buffer Tool:
All created buffer features are added to the Shapes Layer.