The good news is that you have a hole in your pot. The bad news is that if it is large, you will want to cover it so that your potting soil will stay in and water can get out. I usually use plastic window screening that I buy in a large roll that lasts me for years. When I need a piece I simply cut it off and place it in the bottom of my pot over the drainage hole.
You can also use a piece of paper towel or a coffee filter. Whatever you do, don't use gravel or pot shards. This was commonly thought to increase drainage, but studies have shown that it actually impedes drainage.
An even better option albeit more expensive is a product called Better Than Rocks which is a plastic mesh that not only covers drainage holes, it also helps keep plants healthy.
Another option is to line your container with moss. I often do this when you will be able to see it. Moss is beautiful and can really add to the look of your container. There are several types of moss you can line a container with. I usually use sphagnum moss which is the easiest to use and you can buy it by the bag.
To line your container with moss, first soak it for at least 5 minutes in a bucket or bowl of water. Then grab a handful and wring it out until it is just moist. Flatten it between your palms and then apply it to the bottom of your pot. If you are lining your entire container, work up the sides from the bottom until the whole pot is covered with a layer of moss. Then add potting soil. An advantage of using moss is that it will help your soil to retain water.