The activity number is determined in this way:
time = number of two-week periods in which you've posted since your registration
activity = min(time * 14, posts)
Activity is updated every hour.
Can someone help me understand it. ELI5 please.
What is ELI5? Simply put you can get 14 activity every fortnightly period you have posted in. You only need to post once in the period then you can collect the potential points later.