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Most people have misconceptions about how flight works, you don't have to understand the details of flight to fly but having a grasp of the basics helps.

As long as the wings are moving forward they will produce lift. Lift is one of the the forces on the glider. The others being drag (friction) and weight (gravity). Weight always pull the glider towards the ground, and drag always tries to slow the glider down.

The lift from the wings pushes the glider up and forward. This lift keeps the glider in the air; unfortunately, as the glider moves though the air, drag slows the glider down. To maintain a constant speed, the glider must therefore fly slightly ‘downhill’. Hence the glider slowly loses height over time. A typical training glider will have a glide ratio of 30:1 (it will lose one unit of height for every thirty it moves forward) while a high performance glider will have a glide ratio of 60:1 or more.

[https://www.youtube.com/watch?v=vJouxKs7T9c This video] on the CUGC YouTube channel explains this.