I understand your confusion. You must realize that experience has multiple meanings. It may refer to single encounters or to collective wisdom. the meanings are as follows : ***************************************************************************************** 1. a particular instance of personally encountering or undergoing something: My encounter with the bear in the woods was a frightening experience. 2. the process or fact of personally observing, encountering, or undergoing something: business experience. 3. the observing, encountering, or undergoing of things generally as they occur in the course of time: to learn from experience; the range of human experience. 4. knowledge or practical wisdom gained from what one has observed, encountered, or undergone: a man of experience. ***************************************************************************************** when we use Experience to mean the 1st meaning given above, we can use the plural form. e.g. I have had many bad experiences of encounter with bears in the woods.

when we are talking about several activities that we have experienced before. experiences means activities that I have experienced before.this s is for number of activities.