The quickest way to file your return is online. 

First of all you will need to register to submit your self assessment online. Once you have registered you will be sent an activation code to submit your return.
Fill out all relevant sections of your return and submit in section 8. Once submitted on the right hand side of the screen there will be options to ‘view your calculation’ and ‘View/Print/Save your Return’. Go to both sections and save the documents needed for your application. 

If you use an accountant you may contact them to do this on your behalf.