Place the pieces on a flat surface and hide the T-shaped piece under the other four.
Cover Up was my entry in the 2019 Nob Yoshigahara Puzzle Design Competition. It was made by Brian Menold of Wood Wonders Online. He sometimes offers copies of Cover Up for sale. You can also buy Cover Up from Mr. Puzzle of Australia. Brian Young of Mr. Puzzle made copies of Cover Up as an exchange puzzle for Rosemary Howbrigg.
I made the set shown above from precut wooden cubes, glue, and acrylic paint.