AxisAlignedRectangles are rectangular shapes which cannot be rotated. AxisAlignedRectangles can be used as collision objects. For information on using AxisAlignedRectangles in code, see the AxisAlignedRectangle code page.
To add an AxisAlignedRectangle to an entity:
Expand your entity
Right-click on the Objects item
Select "Add Object"
Enter the name "Collision"
Set the SourceType to "FlatRedBallType
Set the SourceClassType to "AxisAlignedRectangle"