Main toolbar > Normal Align (on Align flyout)
Tools menu > Normal Align
Keyboard > ALT+N
The Normal Align button, available from the Align flyout, uses the Normal Align dialog to align the normals of two objects. To see the Normal Align dialog, select a source object, then a normal on it, then a normal on a second object. Upon releasing the mouse, the Normal Align dialog appears.
In a mesh or loft object, you can use this to align faces. You can use Normal Align with any selection that can be transformed.
If you use Normal Align while a sub-object selection is active, only that selection is aligned. This is useful when aligning sub-object selections of faces, since otherwise there's no valid face normal for the source object.
Normal Align respects smoothing groups and uses the interpolated normal, based on face smoothing. As a result, you can orient the source object face to any part of the target surface, rather than having it snap to face normals.
For an object with no faces (such as helper objects), Normal Align uses the Z axis and origin of the object as a normal. Thus you can use a Point object with Normal Align.
From this flyout you can also choose Align, Place Highlight, Align to Camera, or Align to View.