Final fantasy style game help

[left]hi[/left]
[left]i have 3 questions to ask[/left]
[left]1.how do you do that when your walking around suddenly a battle begins[/left]
[left]of course with always different monsters[/left]
[left]2.how do you do that when youve attacked that the enemy attacks after[/left]
[left]with different attacks always and maybe items of course[/left]
[left]3.how can i do that you can always attack a different monster?[/left]
[left] [/left]