Tablet [Q] Unfortunately app has been stopped

Hi to every one. i am a newbee and want to develop some comprehensive apps. i got some problem here while developing a testing app. everything is fine. i got no errors in code. but when ever i tried to run the project on emulator or to the real device. i suddenly got an error saying " Unfortunately app has been stopped". what does that mean. i am using eclipse and setting environment properly. working on API level 19 which is by default downloaded with the eclipse package in latest versions. and not any else API has been downloaded by me.
WHAT I Suppose to do right now. want some realtime and reliable solution to this problem.
Com'on devs .. answer please..