Can anybody explain what is potential activity? The difference between the number of posts and activity?
Not really. You only need to make one post to be able to collect the full 14 activity at a later date. So if you made one post each in two seperate periods you would have 2 posts and 2 activity but a potential activity of 28. Once you made a total of 28 posts you would then get the full 28 activity but no more until the next period.
Do I still need to make 28 post to earn 28 activity or just make 2 post will earn 28 activity as long as I made that post on 2 separate periods
It depends on the number of posts you have since it will cover up those potential activities. For example, you have 43 posts and in the next acitivity period you are suppose to have 28 then all you need to do is just post atleast one to get your activity updated (which is in hourly basis). Another scenario, you have 16 posts and next activity period your suppose to have 28 activities yet you only post one so that means you will have 17 activities and 11 potential activities.