The difference between erosion and weathering is that erosion involves movement while weathering takes place without movement. Both processes are involved in the decomposition of rocks.
There are two kinds of weathering, mechanical and chemical. Mechanical weathering breaks rocks into small pieces and fragments. Chemical weathering changes mineral structures inside of rocks. The pieces of rock fall off, but the rock itself stays put during both types of weathering processes. Erosion, which is also called mass wasting, happens when the weathered pieces of rock roll down-slope, along with another agent, such as in the case of a mud slide or moving ice floe.