In this days all the casinos online have very nice offer with very high casino bonus, but there are those online casinos that do not credit due bonuses earned by players; delay or default in remitting withdrawals asked by players or otherwise renege on their commitments.
The simplest way to identify this casinos is to check out the blacklist of online casino watch dog organizations.
Also one of the best way in identify the best online casino is sharing information with other players. There are several online forums and message boards where online casino players share experiences.
After you do that then you can make a account to deposits some moeny, then you can play the games.
Good Luck!