A deep ½" socket will be required to tighten these nuts. The (fixed) nut at the other end of the rod may need to be restrained. Usually this can be done with a standard ½" socket and an extension bar. (See next photo.)
If your press arrives with the rods already inserted, place a nut and washer on each thread and tighten. It is important that you leave an equal amount of thread exposed beyond the nut at each end; when tightening, alternate between opposite ends to keep the rod centered. Do not over-tighten.