The steamer basket needs to have a flat bottom and either a set of legs that holds it away from the bottom of the pot, or a rim so that it can sit on top of the pot. You can use the same pot-and-steamer basket combo, or you can use a pot-and-glass dish combo instead. The cakes may look a little different from each other when you finish, but they will still taste the same.  The baking times will be the same for both set-ups. If you don't do this, then you'll have to bake the cake in batches. Just like preheating an oven, you need to preheat the pot. Simply cover the pot with a tight fitting lid, turn the heat up to high, and wait 5 minutes.  If you don't do this, it will be like sticking a cake into a cold oven; the cakes won't bake properly and may come out under-baked.  Make sure that the lid fits snugly on the steamer basket or glass dish. You don't want any steam to escape. This will be especially important once you add the cake.

How would you rephrase that briefly using Vietnamese?
Chuẩn bị nồi và xửng hấp hoặc khay nướng thủy tinh. Chuẩn bị thêm một nồi hấp cách thủy nếu bạn làm nhiều bánh. Đậy nắp nồi và đun nước với lửa to khoảng 5 phút.