Friction is caused by the interactions between the sometimes microscopic roughness of different substances. As a result, friction is primarily affected by the "roughness" of an object. Friction is also affected by the mass or weight of the object as well.
Frictional force is proportional to the normal force on an object. To understand the normal force it is important to consider that all forces have an equal and opposite force. In other words, when an object sits on the ground, gravity acts on the object, the object pushes against the ground, and the ground pushes back up. Heavier objects have more friction. Rougher objects also have more surface area. This means that there are more opportunities for the surface to interact with whatever it is rubbing against.