When you have varus knees, it's commonly known as "bow-leggedness". This happens when one or both knees start to bend out to the side, causing excess strain and pressure on the inside of the knee. Most often it causes early onset arthritis, but can also lead to issues with the meniscus and ligaments.
Wearing a knee varus brace doesn't correct the misalignment (for anyone past adolescence, this can only be done by surgery). However, it can greatly alleviate the pain and discomfort the varus causes, and by wearing a varus knee brace, you can slow down or even stop the damage it's doing to your joint.