UVB rays cause sunburn and are mostly blocked by cloud cover and glass. UVA rays are different: present year-round at consistent strength, they pass through both, and they're responsible for most premature aging. If you drive, sit near a window, or walk between buildings, you're getting UVA exposure with no sunburn to warn you.
What it looks like
SPF 30 or higher, applied as the last step of your morning routine, on face, ears, and neck. It's the single step with the biggest long-term impact on how skin ages, and it takes fifteen seconds.