Answer: By desire! The Creator created desire and He fills it. A desire and a filling are the small bricks that all the worlds are built of. The whole world is made of these small bricks, small desires. When they come in contact with each other and connect, they create worlds, just like we build buildings from bricks.
When this Partzuf connects with other Partzufim it is called a world. The worlds connect to each other and create reality. This is how it works.
From KabTV’s “Fundamentals of Kabbalah” 4/21/19