Gravity is the force that pulls everything down to the earth. Gravitational force pulls everything to the centre of the earth. The bigger the mass, the larger the gravitational force. Without gravity we would all float off into space.
Drag is the force that slows the movement of an object through air or water. As a moving object pushes the water and air out of the way, the water or air pushes back on the object. This drag force is always opposite to the way the object is moving. The drag force increases as the object moves faster.
Thrust is the force that moves an object. When flying a kite, the thrust comes from wind. The thrust must be stronger than the drag to make the object move.
In a plane, thrust comes from your legs.
Lift is the upwards force on the kite. Lift is created by air flowing around the kite. The different speeds of the air flowing around the kite make it lift into the air.