Welcome to the forum,I would suggest that you use the search function as this subject has been answered many many times.
What you are referring to is a feature of the F1 visa - OPT - Optional Practical Training. You have to complete the academic course and then may be eligible if offered, the ability to undertake the OPT for a maximum of 1 year.
As it says - it is 'optional' - no guarantee and if offered, you wont accrue many hours in that year (if that is your aim).
You also have to pay your own expenses during that year so make sure you have a bucket load of money available.
At the end of the year OPT, you have to leave the US.