What is the rule of power play in cricket?

Powerplay is a rule in which the only 2 or 3 fielders can should be outside the 30 yard circle.....This is an advantage for the batsmen to score quick runs. There are 3 powerplays in one day cricket,the first one is commpulsory for the first ten overs, and the 2nd and the 3rd powerplays are 5 overs each.....T20 cricket one compulsory powerplay for the first six overs........