Purpose
Avoid the discomfort of having to squint at the sun. Or remove glare from either the computer screen or from reflected light. Or improve visibility at night.
Choices
Buy some light safety glasses which fit over prescription eye-glasses, with either smoke or yellow tinted lenses. Sunglasses should ideally cover the entire visual range where the sun strikes the eyes: even the top. For this reason, clip-on sunglasses are inadequate.
Or Use Prescription sun glasses or sun glasses which fit over glasses.