It would help to know what device you are asking about. It would also be helpful if you used punctuation.
Somewhere on your phone/tablet there should be a way to view battery stats. For example, in Honeycomb it is found under Settings > Applications > Battery use; on an AT&T S4 there is a Battery Manager app in the drawer that provides the same info. Highest usage items are listed at the top. You can use this info to determine what needs attention. Unless your device is off more than on, it's normal for the Screen to be #1 on the list. You can turn down brightness or use auto-brightness, but it will still likely remain the #1 battery drain. There are other things you can do, like disabling wifi when not in range of a wifi ap, setting account sync to a longer time interval, etc. If it only happens occasionally, I'd suspect that some service is remaining running after using an app (e.g., Navigation). You can check this in Settings > Manage apps > Running. Finally, if it continues to be a problem, there are apps that can help, such as JuiceDefender.
