You can make your own henna, or you can save yourself time by getting some at a Middle Eastern or Indian grocery stores. But enough henna to cover your hair. 200g is usually enough for shoulder-length hair. If you want specialty henna, you may have to visit a henna artist. If you have light-colored hair, then you will need to use henna as a base. You should put a small amount of henna in a bowl. Pour a small amount of hot water into the bowl. Then, mix in some lemon juice or vinegar. Stir this mixture till it gets thick. Keep adding liquid until it has a creamy type of thickness to it. Once it’s thick enough, you should wrap the bowl with plastic wrap. You want the henna to be warm when you apply it to your hair, but not hot. After several minutes, take the plastic wrap off the bowl and test to make sure the henna is no longer hot. You don't want any of the henna to get on your face or ears while you're dying your hair. Any kind of thick cream or conditioner will work. You want to place a large amount of henna paste on your hair. It should be so thick that it goes down to your scalp. Once you’ve placed a substantial amount of henna on each section of your hair, wrap plastic around your head. You should not remove this wrap for two to four hours. Doing this will make sure that your hair absorbs the henna completely.

How would you rephrase that briefly using Vietnamese?
Mua hoặc làm bột henna. Trộn bột henna. Chờ vài phút cho henna nguội trước khi sử dụng. Thoa kem lên tai và đường viền chân tóc để bảo vệ da. Thoa henna lên tóc. Trùm đầu.