Cut. Sand. Oil. Paint (if required). Assemble.
Simply push the Leg tennon into mortice in the circular top (seat/table). Can be inserted in either direction so leg is flush with circumference or will leave a 1" lip - your choice of preference. Do this for all four legs.
For additional strength you may wish to glue these - or leave as tension/pressure fit for easy disassemble. (if using as a seat/stool I would recommend the glue for additional strength).
As been designed to cut from one piece of wood 24" square but would look good cutting from different species to add contrast. Alternatively could paint for same effect.