Drip 2-3 drops of your chosen essential oil into the foam sponge in the top piece. The top piece is then attached to the nozzle on the machine. The steam will now seep through the foam sponge and the selected essential oil will be infused into the steam. NOTE: Do not drip oil directly into the water tank. Drip oil only on the applicable foam piece. The foam sponge can be rinsed with water and dried afterwards, so that it is ready to have another oil added at the next treatment. However, three top pieces with foam sponge are included, so you can easily switch between different oils.