What happens if you break out of the prison?
I assume that you're asking what happens if you get caught. Of course, if you break out of prison the first thing that happens is that law enforcement officials try to track you down. If they catch you, you are generally (this can vary by state in the United States) charged with the crime of escape.
The punishment for this varies by state also. But for example, in Virginia, if you escape by "force or violence" (other than by setting fire to the prison) you are guilty of a Class 6 felony. A Class 6 felony is punishable by a term of at least 1 year in prison but not more than 5 years. That term in prison starts after your original term ends.
But again, it varies by state.
Is that what you're asking?
Whether or not one gets caught after escaping from a prison, it is a criminal act punishable law. A person who escapes from prison is liable punishment in addition to remaining period of the original jail sentence. In addition, the person also forgoes the the benefit of remission in original jail sentence for good conduct.
Laws of different countries and different stated within a country may have differing terms of imprisonments and other punishment for escaping from the jail. The punishment is also affected by the method of escaping from jail. For example, if a murder is committed in the process the person becomes liable to be punished for murder whether or not the attempt to escape is successful. And to that extent, the mere act of attempting to break out of prison is an illegal act, even when such attempt is unsuccessful.