Fit Note, What to do with it ?

Okay I went to the doctors today and he gave me a fit note (sick note) which basically says I am not able to work for one month.
I am not in work and haven't been before (I am only 19). Also I am not on any benefits at the moment so I have no idea what I do with this.
I know I need to fill it out
but where do I need to go from there ? My doctor didn't mention anything about me going to the job centre.
Basically I dont know where to go from here with claiming.
Please could you help
Also if you need any more information let me know.