Mints are difficult to grow by seeds due to low germination rate. Mixed flavored varieties can be grown by seed sowing. Sow the seeds in a seedling tray, fill it with suitable quality sowing medium like coco-peat. Later transplant the young seedlings in pots and containers.
Take some stem cuttings from a Mint plant of the desirable variety. Dip the cuttings in a bowl of water and add some soil in it. This will encourage the root formation. Once the roots appear, you can transplant the cuttings into pots, and they will start growing just like a new Mint plant. Read about growing plants by stem cuttings.
If you don’t have any Mint cuttings or seeds, it is not a bad idea to buy new Mint plants from your local nursery. Please make sure that you buy the right variety of Mint.