With this mod you get a car with no tyre wear, no fuel usage, only 1 kg of fuel so you have incredible race pace. 4x powerful ERS with instant recharge under braking and basically unlimited deployment and harvest. Using the Standard setting gets the most performance in order to keep the user quicker than the AI teammate. For a more realistic pace use the Overtake setting. All other ERS settings have no deployment. The best strategy to use in races is to start on medium tyres and to pit for soft at the end of lap 1. The AI teammate will start on softs and pit on the next to last lap. This mod can be used in career mode but the performace bars will not reflect the pace of the car. You can still upgrade the car in career mode.
Then you need to open the ERP file, click XML files on the lower row of tabs. Choose the team you chose (unless it's Mercedes in that case you need to add the file to every team including the FOM Car file because there is a Merc file in every team for some reason). After you click the team you want, click the XML files tab at the top and choose the file you downloaded. Then click save and it should be good to go! Let me know if you have any other questions :)