To see who among your friends need help with an order on their Orderboard, tap the Friend button on the left side of the game screen, then tap on the request icon located at the upper left of the screen.
Next, sort your Help Requests by selecting "Orderboard Requests" from the dropdown menu to show neighbors that need your help.
Tap your neighbor’s profile, then tap OK to visit your neighbor.
When you're on a neighbor's farm, you will see a bubble with a purple Ask For Help icon on top of their Orderboard. A green checkmark on the bubble indicates that you have the required items to help your neighbor out and fulfill their order.
After tapping the Orderboard, you can select the Ask For Help order and fulfill it using your own items by tapping the Help button. You will receive the Coin value of the order and a Help bonus as your reward. By helping your neighbor, any of your ongoing tasks or quests that require this order will also progress.
If you are a member of a Co-op, you may also see requests for help in the Co-op chat, and by tapping this message, you can visit your neighbor's farm to help them out with their Orderboard.