Below is a guide on the Use Furniture task in Rune Factory 5!
Client: Ryker
Objective: Customize some furniture for your room
Reward(s): Storage Box x1
After accepting this task, Ryker shows up and gives you a Storage Box along with explaining how to place items in your room. You can now move it around where ever you please (picking it up and setting it back down also counts). Once you’re done, return to the Task Board to receive some final words from Ryker, completing the task.