What is the difference between erosion and agents of erosion?

Erosion is the result of something that is still not controlled. Agents of erosion when we are talking about soil, for instance, could be the wind and water or even lack of vegetation, poor soil.

Definition of erosion by 'the free dictionary" :

1. The process of eroding or the condition of being eroded: erosion of the beach; progressive erosion of confidence in our legal system; erosion of the value of the dollar abroad.

2. The group of natural processes, including weathering, dissolution, abrasion, corrosion, and transportation, by which material is worn away from the earth's surface.

You can notice that "erosion' has two main meanings.