The Order Board is on the small dock where you see Kate and her boat. Tap on the Order Board behind her to open it and see guest orders.
Orders come from guests staying at the guest bungalows. Each order shows how many coins and how much XP you'll receive from filling the order.
A green checkmark means that you have all the Goods needed to fill that order.
Tap on an order and the desired Goods appear on the right. The number on the left shows how many of that item you have. The number on the right is how many you need to fill the order.
In addition to coins and XP, filling guest orders can sometimes give you bonus rewards, such as Storage Parts or Tools.
Tap the Deliver! button to complete the Guest Order. Kate delivers orders to the bungalows. The timer shows when she'll be back. A new order has immediately taken the place of the order that was just sent out.
Some guests are more trouble than they're worth! Tap on the red trash can button to trash an order. After a waiting period, a new order will take its place.
When Kate returns, she has the reward for delivering the order on the back of her boat. Tap on the boat to collect your rewards.