Well, the activity bars show how active you have been over the past month, or 28 days rathers. The stars are only shown on you account and only so that you can see it. The first red star means that you have logged in for the day and got credit for that, and the other 4 are for the amount of posts you have that day, with a max of 4 posts per day for max activity level percent raise.

If you put you mouse over the activity bar it will show you what your activity level currently is to date.

There are threads about this in Forum Discussion, entitled Death of Post Counts made by WW that explains this more thoroughly if you want to know more.