The subunits are divided by the double red lines. Make these A, B, C sections separately, leaving a 1/4" seam allowance around each subunit. Then assemble by sewing B-unit to C-unit, then sew those 2 to the A-unit.
This Boot Block was adapted from a boot block in the Sew Precise!TM Collection 3 set of blocks sold by Electric Quilt. The Sew Precise! collection has other fun shoe blocks in it, too.