Hi Denise, Here is a video to show you how to do it.
The first thing I would check , is to see if you need to replace the washer ...
Yup... check the washer. Be sure to turn off the water supply to the faucet first. Depending on the style, you may get an unwanted shower if you don't! ;) (speaking from experience!) LOL
It depends on where the faucet is leaking. If it is dripping from the faucet head, then I'd first try replacing the old washer with a new one. Easy peasy. If it is leaking near the base of the faucet, near the sink base at counter level, a replacement of that O-ring might be the answer. In either case, go to youtube.com and enter a leading question and you'll find many tutorials there that will help you learn the process.
Hi Denise: Here's my 2 cents:) and 2 sites to check out:
https://www.thespruce.com/fix-a-leaky-faucet-4103580" rel="nofollow noopener" target="_blank"> https://www.thespruce.com/fix-a-leaky-faucet-4103580
One important thing to do, after turning the water off and letting the faucet run until it stops, is when you are disassembling the faucet, get a hand towel, and a nickle. Lay the towel out flat and when you take something off, lay it on the towel. The first thing should be at the upper left, and everything after that should go to the right, just like you took it off. Get your phone out and take a picture of the washer just like you took it off, i.e., the narrow end down or up or whatever. A picture will remind you of how it came off. Then, take everything else off until it's empty. Use a rag to clean out the area and get all of the water out. Then, take the washer and put it in your pocket. Put the nickel where the washer was so you know which part it goes on after. Take the washer to the hardware or home improvement store, match it up and start to put the faucet back together, starting with the last piece you took off. When you get to the washer, look at the picture on your phone because you know you forgot which end goes down:) Snug everything down, turn on the water and see if anything squirts out. If not, then turn on the tap and check for leaks. You can do this, I have faith in you! Good luck