To sell a used car online, you should first take clear, high-quality photos of both the exterior and interior of the vehicle. This will help potential buyers get a good sense of the appearance of the car. Next, create a detailed description of the car, including its make, model, year, and any unique features or upgrades. This will help buyers understand the specifics of the vehicle and decide if it meets their needs. Once you have these materials ready, you can list/advertise the car for sale on a website or app that allows users to buy and sell vehicles. Finally, set a fair asking price and provide contact information so that potential buyers can inquire.