To access the market stalls menu you would need to select farmers market from it's pull down menu. Inside you can see what bushels you've collected from your neighbors under the my bushels section. What bushels your neighbors have available in the get bushels section and what bushels your stall is currently offering in the my stalls section. Clicking the get bushels button will show you what bushels all your neighbors are currently offering. Clicking any available bushels will display a list of bushels that each neighbor has available and how long their stall is open for. Selecting a specific neighbor will take you to their stall. Bushels taken from your friends stall are added to your inventory and can be seen in the my bushels section of your stall.
Once you collect bushels either from your farm or your neighbors they are all stored in your inventory. You can hold up to 50 bushels in your inventory. Each bushel can be shared or used. Clicking the "Share" button on any bushel will allow you to offer up a number of bushels of your choosing to your friends via a feed. Clicking the "Use" button consumes one of the bushels and gives you a bonus. The type of bonus will depend on whether you have access to the crop or not. If the bushel used came from a crop that you did plant you receive a bonus of +1 mastery whenever that crop is harvested on your farm for two hours. If you have already mastered this crop the bonus is +1 Experience Point per harvest. If you use the bushel of a crop that you are not high enough of a level to play in you'll receive a licence to plant that crop that lasts for 2 hours. Whenever neighbors use your stall you can choose to receive a reward of your choice. If you neighbors have used your market stall an arrow will point to the appropriate stall. Viewing the interior of your stall will show you the three rewards that you can choose from. Coins, Fuel and Experience Points (XP).