SPF (sun protection factor) indicates how well a sunscreen shields skin from UVB rays, the main cause of sunburn. "Broad-spectrum" products also protect against UVA, which drives much of photoaging. Higher SPF offers more protection, but no sunscreen blocks 100%, and regular reapplication matters.
Daily broad-spectrum sunscreen (commonly SPF 30 or higher) is the single most effective anti-aging step — most visible skin aging, including wrinkles, sagging and hyperpigmentation, comes from cumulative sun exposure — and it lowers skin-cancer risk. See sunscreen and skin aging.