It's about how the activity has benefited you, and how the collection of activities have resulted in your enhanced capabilities and competencies. You could benefit from attending a training course, but you could also benefit from reading a book or indeed from a work assignment that stretches you.
This approach is called reflective learning and focuses on the benefits you gain from the mix of activities you complete or plan, rather than gaining defined points or simply committing units of time.
What is key is to identify the benefit to you as a result of the CPD activity and to place this in the context of your career aspirations. You identify your development needs - what you need to develop and when. BCS supports you by providing information, guidance and the resources to help you achieve them.