Wendy,. Pour about 1/2 cup of baking soda down your drain, pour vinegar over that, but cover it because it will fizz. If you have a round rubber jar cap remover, use that to cover the drain right after you pour the vinegar. Then run hot water down the drain. If this doesn't work, you might need a commercial cleaner, like Draino. Aloha!
Did you try plunging first?
Is the drain in the bathroom or kitchen. If you have a problem in the kitchen, I use around a half cup baking soda, follow this with a cup of vinegar. Let it fizz and do its work for ten or 15 minutes. I don't plug the drain, it isn't really necessary. I then pour in about a gallon of boiling water to rinse everything down. If it is really blocked, try again. If that doesn't help, try looking at making sure the elbow isn't blocked by something that won't wash down, if that isn't the case, you may need to get someone to rotorooter the drain, it may be blocked down too far. In the bathroom you can do the same thing, but you will need to clean out the hair first. I use a zipit tool that is a thin plastic stick with barbs on it (real cheap and lasts for years), it pulls out the hair. Get out as much as possible, then do the baking soda/vinegar/boiling water hack. I hope this helps you get your drain draining Wendy!