Manipulating USD data natively
Editing USD Properties
UsdAttributeSet - The same as AttributeSet but for native USD. For USD, attributes are one type of Property that a prim may have.
UsdRelationshipSet - Relationships are the other type of Property a prim may have. They are specifically Properties that point to other Properties or prims, eg. Material binding, light linking etc.
UsdMetadataSet - Used to assign metadata to a specified prim.
UsdPrimvarSet - Used for creating primvars. Primvars are data attached to geometry that can interpolate a value (eg. color) over surfaces or volumes to achieve variation. The interpolation type can be chosen, eg. faceVarying - varying values on each face, vertex - values are interpolated between each vertex.
UsdSchemaSet - Can be used to assign a schema API to a prim.
Manipulating USD Data in the Scene
UsdTransformSet and UsdTransformEdit - Transform USD prims.
UsdVariantSet - USD layers can contain variations (eg. geometry/materials variants). This node is used to select a variantSet (eg. character suit colour) and variant (eg. red) for the specified prim.
UsdActiveSet - Used to define what is included in the stage composition. Inactive prims are removed from the stage in a non-destructive way so they are not visible in the Viewer or renders.
UsdToKatana - Used to bring certain elements from USD into Katana so they can be manipulated eg. to use NME, to inherit a light into a GafferThree to make edits.