This puzzle is part of the family of different “6-Piece Burr Puzzle” configurations. This is a “Level 1” design because one piece needs to be moved (“unlocked”) before you can begin to disassemble the puzzle. Disassembly is tricky, but reassembling is much harder!

See here for video:
See here for stable download:

Can’t figure out how to fit the pieces fit together?
See here for an instructional model:
And here for an instructional video: