Article in English: Even if there's no visible dirt you should always wash them under fresh running water to rinse them of any pesticides or lingering bacteria. With your hand, gently rub the skin of the zucchini while holding it under water until it no longer feels gritty. Remove both the stem end and the flower end of the zucchini with a sharp paring knife. If the zucchini is greater than 2 inches (5 cm) in diameter then the seeds may be large and bitter. If this is the case then carefully split the zucchini from end to end, lengthwise. Hold a spoon firmly in one hand and the zucchini in the other, run the tip of the spoon down the zucchini with gentle pressure to remove the seeds. If your zucchini are smaller then you're ready to grate them.

Summary in Vietnamese:
Rửa bí ngòi. Cắt bỏ hai đầu. Bỏ hạt.