iPad 2 has auto lock feature which would automatically lock the iPad after the defined period of idle time reached. But if you want to disable the auto lock then you can change the settings using the General Options.
From the home screen select General Settings.
In the General Settings, navigate to Auto-Lock option
The following Auto-Lock options with different time period would be displayed.
Select Never from the list of available option and this should turn off the auto lock feature in iPad 2