The molecules that form a solid are bonded tightly together with little to no space between them. They vibrate in a fixed position but they don't have room to move around. They additionally have a definite shape and volume.
Liquid: There is more spaces between the particles than there is in a solid. This ensures that the molecules have room too slip past each other and cause the fluid to flow. There are some attractive forces keeping them from moving apart from each other. Additionally, because it is a fluid it can take the shape of containers.
