What does each activity of interest mean?
The data capture process is usually triggered by a business activity. Data must be collected about three facets of each business activity.
1. Each activity of interest 2. The resources affected by each activity 3. The people who participate in each activity

Question

What does each activity of interest mean?
The data capture process is usually triggered by a business activity. Data must be collected about three facets of each business activity. 
1. Each activity of interest 2. The resources affected by each activity 3. The people who participate in each activity

Answer

In this case, "each activity of interest" means each activity you are concerned with, or interested in.