We've provided you with gravel for the bottom of your tank, and growstones to grow your plants in on top of the tank. Growstones float, whereas gravel does not. This is one surefire way to know you've got them in the right spot.
If you have any other questions please feel free to reach out, also we'd love to see your setup once you have it all decked out :)
PS: In addition to decorations, a small tank heater can be a great add. Tropical fish are happiest in warmer water (75-82 °F, 24-28 °C), so if you live in a cooler climate please consider it!