A patch is a saved section of flattened surface. Viewing patches switches the view to a flat 2D mode in which some of the controls don't work.
When making cuts and flattening a surface, you can then save out the resulting section of surface as a patch.
Use the File->Patch->Load Patch... item to load a patch file.
Use the File->Patch->Save Patch command to overwrite the original file, or File->Patch->Save Patch As... to save a new patch file in a new location.