Lying on your back with a pillow under your head.

Anterior: Tighten the muscles around the front of your pelvic floor, as if to stop yourself passing urine. Hold for the prescribed length of time and repeat for the prescribed amount of reps.

Posterior: Tighten the muscles around your back passage as if to stop passing wind.
Hold for the prescribed length of time and repeat for the prescribed amount of reps.

Aim to do both techniques together, holding for the prescribed length of time and repeating.