Please follow these steps:
1. Visit the first village, then enter the market by clicking on it.
2. On the page that opens you will see all current offers. Underneath, you will find two options. Under "product overview", you can select all offers of just one product - all offers for carrots, that are currently on the market, for instance, and the prices that they are selling for. Click on "show my market stall", to see your own market stall, and to sell your own products.
3. Drag the product you would like to sell to the sacks on the right hand side. That is, click on them with your left mouse button, pull them over with your mouse, then let go of the left mouse button when you are exactly above the sacks.
4. A window will pop up, asking you to name the amount and price. Make sure you check the current market prices, before you enter the amount of money you'd like to sell your plants for. You can do so in the market overview.
5. Click on "offer at market now".
6. You will be charged a 10% market fee for each offer. Click "ok" to accept the sales fee, close the window if you don't want to pay it. Your offer will not be put on the market in that case.
7. Once your offer is on the market, you can see it on the right hand side. Click on the "x", if you'd like to take it back from the market. Note, that you won't be returned the 10% market fee, though!