Place the split red lentils into a sieve or fine-holed colander. Split red lentils are notorious for having debris in them, so be sure to clean well. Rinse under running water and pick out any obvious large pieces of debris. Add the water to the pan. Be sure to stir now and then to prevent sticking to the saucepan. The red split lentils will be cooked in about 25 minutes. You'll know they're done by observation - they turn into a mush or thick puree.  Cooked split red lentils tend to be added to other dishes but can be eaten alone if you like them. Try them with the following ideas:  Use them to thicken soups and casseroles. Add them to vegetable or meat curries. Turn them into kofte.

TL;DR in Vietnamese:
Rửa sạch đậu khô. Cho đậu đã rửa vào nồi để nấu. Giảm nhỏ lửa khi nước sôi. Bắc nồi xuống khi đậu đã chín. Nêm nếm với muối và hạt tiêu. Dùng đậu lăng cho món ăn thích hợp.