Sugar vs. “added sugar”

Hi, Brooke. Am I correct that when reading labels, it’s not the “sugar” content listed in the table that matters as much as the contents list? Plain yogurt (at least the brand I buy) has no added sugar, but still has it in the table. If something is okay for a diabetic (“sugar free”) does that mean it’s okay? (Not talking about candy and junk–looking at healthy foods.)