The Oak kitchen table can be built in a Kitchen hotspot of your player owned home. To build the Oak kitchen table you'll need 3 oak planks or a flatpack item discussed below. Remember to have a hammer and saw in your tool-belt or in your inventory when building.
You can place items on your kitchen table but they will disappear after a certain amount of time, just as if you dropped the item on the ground.
The Oak kitchen table flatpack item can be made on a workbench in the workshop of your player owned home. To make the flatpack version you'll need 3 oak planks, along with a saw and hammer as if you were building the item. The saw and hammer can be in your tool-belt or in your inventory.
You can sell the flatpack item at the Grand Exchange or to other players for money. Alternatively, if you've completed the hard Fremennik Tasks you can speak to Advisor Ghrim on Miscellania who will buy the flatpack item from you.