A dripping faucet almost always must be disassembled in order to replace internal O-rings, seats, or washers. With some you replace the entire cartridge. There are many types and styles. The only way to know what you need is to shut off the water below the sink and then disassemble the faucet. This video shows how to do that with a traditional stem valve type: https://youtu.be/wPGFWtVhzYo you'll find YouTube videos showing how to deal with almost any type of faucet. Good luck!