Make sure you don't fill it up all the way. You will need to leave some space at the top of the bowl so that the saltwater doesn't splash into your freshwater receptacle.  Make sure your bowl or container is watertight. If it is leaking, your saltwater will drain away before it can form steam to condense as freshwater. Make sure you have plenty of sunlight because this method takes several hours. Do this slowly. If you do this too quickly, some saltwater might splash into your cup. This will contaminate your freshwater as you collect it.  Make sure the lip of the glass remains above water. You might need to weight it down with a rock to prevent it from sliding around. Make sure the wrap isn't too loose or too tight. Be sure that the plastic wrap has a tight seal on the rim of the saltwater bowl. If there are any leaks in the plastic wrap, steam or freshwater vapor might escape. Use a sturdy brand of plastic wrap so it doesn't tear. Do this just above the cup or container in the center of the bowl. This will cause the plastic wrap to dip in the center, allowing fresh water to drip into your cup.  Make sure your rock or weight isn't too heavy or it will tear the plastic wrap. Make sure the cup is in the center of the bowl before continuing. This will heat the water and cause condensation to form on the plastic wrap. As condensation forms, freshwater droplets will drip from the plastic wrap and into the cup.  This will allow you to slowly collect freshwater. This method takes several hours so be patient. After you have enough freshwater in your cup, you can drink it. It is safe and completely desalinated.

TL;DR in Vietnamese:
Đổ nước mặn vào bát hoặc hộp. Đặt một chiếc cốc nhỏ hoặc hộp đựng nhỏ vào nước mặn. Đậy kín bát bằng màng bọc nhựa. Đặt một viên đá hoặc vật nặng ở giữa bề mặt của màng bọc, ngay phía trên cốc hoặc hộp đặt ở giữa bát nước mặn. Đặt bát nước mặn trực tiếp dưới ánh nắng mặt trời.