Click on your profile and you will find your point balance , when you earn 1000 points it is equal 1$ , each 1000 points is 1$, to make a withdrawal you should earn 2000 points which is 2$.
For the old amounts you recieved, you can check your skrill or PayPal account or emails you recieve to know how much you earn since you started.
After reaching 2000 points if you withdraw the 2$ , you will start again and the points start to count again from zero because you already recieved the money for the old points.