It depends sometimes on the teacher and the text-but often it simply means language techniques. In a particular novel a writer may use a circular structure in that it starts and ends at the same place. They may have different narrative voices or use flashbacks. They might use letters or diary entries here and there. These could be considered structural techniques. In a poem it might refer to a poet's decision to use a sonnet structure and iambic pentameter for example. Hope that helps.
^ This. Poems are the easiest for structural devices like a consistent number of lines in a stanza, metering, rhyming scheme, etc. But it does depend on the text type.