Binder: Drag the subordinate document on top of the main document.
Outline: Ditto but once there is one child you can drag others in line with the revealed first child.
Corkboard: I may be corrected, but I don’t think you can assign hierarchy in the corkboard though the icon at the top left of the card will show whether the card has children. Ah! You can Group items (subsume them under a folder).
Cmd-Ctrl-Arrow keys to move an item up, down, right and left.
Ctrl-Up/Down will jump between items which are acting as parents to other items. This could be stacks of documents or folders, it doesn’t matter. There are also Group and Ungroup commands in the Documents menu, which should be familiar to outliner users.