Disintegration - The process of rocky material breaking into pieces.
Decomposition - The process of organic substances breaking into pieces.
Weathering = Disintegration or Decomposition or both - in situ (with little or no movement)
Weathering could be due to mechanical processes (frost action or frost shattering), chemical processes (water dissolving limestone), or biological processes (plants breaking up rocks).
Mass wasting - Transportation of rocks, soil, debris down the slope by gravity with no or little help of transporting agent
Erosion = Transportation of rock material by water, wind, glaciers, waves, or gravity.
Denudation = Weathering + Erosion = Slopes (the land) being reduced in height and their shape modified.
So first happens the disintegration and decomposition of rocks in situ - these together are known as weathering - when the weathered material is transported from one place to another - this process is known as erosion - the effect of weathering and erosion is denudation (lowering and modification in shape) of earth's surface/landforms).