Gravity is an attractive force that is present between any object that has mass.  The earth has mass and therefore an attractive force toward all other objects in the universe that have mass.  Earth is the planet on which we all live.  Earth is located in space within the solar system.  The solar system is contained within the Milky Way galaxy.  The Milky Way and the Solar System both exist due to the fact that gravity attracts massive objects together.  The force is proportional to the distance between the objects.