Mint does not germinate from seed too easily, so only the most experienced gardeners should start from seed. Plant directly into potting soil or compost after you bring it home. A garden store will have more varieties of mint; however, you may be able to find mint seedlings and plants at your local farmer’s market and supermarket. Ask a friend if you can harvest from an existing mint plant or find one in a local garden. Cut approximately 1⁄2 inch (1.3 cm) above a stem junction with sharp scissors. Make sure the cutting is at least 4–6 inches (10–15 cm) long and remove most of the leaves. It is not guaranteed that you will be able to grow a plant from each cutting, but it is a good way to use leftover mint if you are willing to experiment. Place freshly cut sprigs in the glass to grow new roots. Keep it in a warm, sunny place and wait for white roots to grow out of the cut stem. Add water as needed to keep the glass full. They can even extend to the bottom of your pot depth.

TL;DR in Vietnamese:
Đến cửa hàng bán cây để mua cây con. Cắt nhánh cây từ cây bạc hà trưởng thành. Sử dụng nhánh bạc hà mua ở quầy hàng rau tươi ở siêu thị. Rót nước vào chiếc cốc sạch. Chờ đến khi các sợi rễ trắng mọc dài vài cm trước khi đem trồng.