The "Solar System" is a "system" consisting of at least eight planets, many dwarf planets, dozens of moons, millions of asteroids and comets, all bound together by the gravity of a large central star.
The Milky Way Galaxy is a system of up to 400 billion stars, stellar nurseries, rotating arms, and a large black hole in the middle that helps hold everything together, again with gravity. Our galaxy is so large with such a large gravitational attraction that it has 1 or 2 other smaller galaxies that orbit around it, and these together also form a system. Groups of galaxies form Galactic Clusters where their mutual gravitational attraction binds them together. The entire universe consists of spiderweb-like strings of galaxies joined theoretically by Dark Matter.
A single atom is also a system, consisting of a large electron cloud bound to a small central nucleus by the electromagnetic force. The nucleus is also a system consisting of protons and neutrons held together by the strong nuclear force, but each of these is a system consisting of three quarks held together also by the strong nuclear force. Groups of atoms form molecules, held together by the electromagnetic force. Large groups of like molecules and atoms form chemicals, coalescing into substances, and these can be combined in different ways to make the materials that everything is made out of.
Your body consists of many different systems working in tandem, but each cell is a very complex system by itself, like a microscopic chemical factory.
The planet Earth also consists of many different systems keeping the whole thing going.
With so many systems from the supergalactic to the subatomic, it gives the impression that there is some sort of design behind it all.