If you mean ‘unfolding’ a curved surface so it becomes a number of facets in a single flat plane, then it can be done by hand - albeit laboriously.
Switch View > Hidden Geometry ON so that you can see any smoothed/hidden edges forming the surface.
Next you need to ‘break’ it somewhere, so select one facet and ‘Group’ it - now any adjacent facets will not ‘stick’ to it when you manipulate them.
Make a Guide-line parallel with an the edge inside this Group, about which you will do the rotation/alignment.
Use the Rotate tool + Ctrl to rotate a copy of that Guide-line at 90 degrees to the original, using the face a an inference for the rotation-axis.
You will use this second Guide-line in subsequent rotation/alignments…
Select all of the remaining facets in the surface which you want to ‘unfold’ flat.
Use the Rotate tool.
Drag its icon along the original Guide-line, holding down the mouse so that the rotation axis locks onto it.
Click on the selected facet nearest the Guide-line and then rotate the selected facets. snapping onto the perpendicular Guide-line.
Now the initially Grouped facet and the adjacent facet [let’s call it ‘A’] are now coplanar.
Select and Move the original Guide-line to the next Edge shared by ‘A’ and its next neighbor.
Select the remaining facets to ‘unfold’ flat - excluding the Grouped facet and ‘A’.
Repeat the Rotation about the Guide-line so that the Grouped facet and ‘A’ AND the next facet [‘B’] are coplanar.
Continue like this until all facets are coplanar… Zzzzzzzzzzzzzzz…
Remember that you may also need to Group other connected facets to prevent them sticking together as you proceed…
BUT - There are alternatives…
Consider a Plugin like like Flattery - available from the SketchUcation PluginStore [updated for v2014], or a tool like Jim Foltz’s older Unfold tool, or MattC’s embryonic AutoUnfold which also lays the flattened result on the ground.
See these links…