He will become eligible for parole automatically, but the exact date depends on his offense.
It's impossible to tell when that will happen without knowing the charges that sent him to prison. Most inmates serve half of their sentences, but if he was convicted of a violent felony listed in Penal Code 667.5(c), he will have to serve 85% of his time.
If he was sentenced to 19 years to life, he will go before a parole board after serving the 19 years. The parole board will review his behavior in prison and the facts of his case, then decide whether to release him. If not, they could delay his next parole hearing for several years. "Lifers" are almost never released the first time they become eligible for parole, and many never get out of prison.
Finally, if he was convicted of certain sex offenses, he will be evaluated before his release to determine whether he qualifies as a sexually violent predator (SVP). If the prison psychologists decide he meets the criteria for an SVP, he would be entitled to a court hearing. If he is found to be an SVP, he could be committed to a state mental hospital until doctors decide he's safe to release.