Gather these parts.  The sizes may vary based on the side of the block, but each will have a top, 4 sides, 4 corner strips, and 4 corner base brackets

Stat by gluing one side into the top as shown.  Make sure it’s as close to a 90 degree angle as possible

Glue in an adjacent side 

Glue in a corner strip as shown

Clue the base corner brace in place as shown

Continue with the rest of the sides and corners