Minecraft wiki entry for Structure_Block, associated text: To load a structure from a folder, simply type minecraft:<folder_name>/<structure_name> ‌[JE only] or if stored at the top level of the structures folder (such as those created in the Save mode) type minecraft:<structure_name>.
Example 1: minecraft:shipwreck/with_mast
Example 2: minecraft:village/snowy/houses/snowy_tannery_1 ‌[JE only]
Example 3: minecraft:my_redstone_contraption