inFamous Paper Trail is an extraordinary set of optional objectives that you can take on while playing the game for the first time or after its completion (having previously completed all the main missions). The distinguishing feature of this element of inFamous: Second Son is that these tasks are performed either in the game (short missions published weekly starting from the game release date) or on several websites related to the project. The benefit of getting involved into inFamous Paper Trail activities is that it gives you an opportunity to gain a lot of karma in the game, through which you can level-up in hero or villain trait more quickly.
The project's main website is http://infamouspapertrail.com/ - I suggest you start by visiting this site and reading frequently asked questions - http://infamouspapertrail.com/faq. You must log on to the website to join the adventure. You can create a new account or use your Facebook account. After you log in and type in basic personal data, you will be directed to the main page. Here it is worth to click on Link your account button. Depending on how you have logged in, either you will be asked for your PSN account data or these will be transferred automatically (if you have logged in using Facebook.)