how is online chess different from live chess?

I normally play live chess, but I would like to play online chess, however I don't quite understand how it works. Is it a live chess game that gives you three days to make your turn? Or is it only updated every 3 days? If you take your turn 2 hours after your opponent takes theirs does their 3 day time limit begin? If a turn is not taken in 3 days does it count as a resignation, and the opponent will be notified?

Is there anyone who can summerize the rules for this type of game?

Yes, it’s just like a live chess game except that you have lots of time to move. Some games can proceed quite quickly though. 

As soon as someone moves their opponent merely has to make a move within the time limit .. doesn’t have to be 3 days; could be 24 hours or 2 weeks.

In live Chess you chose your own parameters

There are plenty of tournaments you can enter, which work the same way. You will find that your “online” rating is about 200 to 250 points higher than your “live chess” rating.