How do I tile over plywood?

can tile over plywood

You might need to add backerboard. The plywood will soak up the mortar and warp.

Put down cement board then lay the tile over the board.

you can paint the plywood with a sealant called Red Guard, this will waterproof the plywood. Cement backer board glued and screwed to the plywood is best, but if you have elevation issues sealing the plywood will work provided the floor is structurally sound enough.

My tiler did porcelain tile right on the 3/4" plywood subfloor. No problem.

you should not lay tiles over plywood . You should do it over cement board