Activities describe your view on all possible economic activities in the world. There are UNO, European standards for activities. However, it is better to define your own classification based on specific business requirements
Activities are different from function. Activities usually relate to a classification of third parties based on the nature of their industry (ex. banking, IT, automotive) whereas function is independent of the activity (i.e. both an IT and an automotive company can have entity which has the function of a warehouse).