Finally, poker is the most difficult casino game of all. There are, of course, many different forms of the game. But even if you focus specifically on Texas hold'em, it takes time just to learn the basic rules never mind actually trying to master the game.
Other players, especially good ones, will make it much harder for you to win. You can consider poker to be the hardest card game to play for that reason. The only way you'll get better is to read a poker guide and practice. I recommend playing online so you can get into a new game in a matter of seconds.