If you are talking about PPF, you should read PPF guide.
In case of employee provident fund, maturity period is 58 years. You can withdraw your full amount once you reach 58 years of age.
You cannot withdraw your amount otherwise. However in certain case you can take advance against your PF balance.
You can withdraw amount for marriage, home loan repayment medical emergency etc. You can also withdraw in case of lose of job. However conditions are that you should have completed 5 years of service. If you are still in job you cannot withdraw money for any purpose other than mentioned above before 5 years.