That's only partially true, and would still be useless if it were totally true. When people say "sugar", they're referring to sucrose, which is half fructose. Even glucose on its own will spike your blood sugar, which will make it harder to burn fat.
Also, your body converts starch into glucose, so starch can spike your blood sugar the same way. Fiber makes your body absorb glucose more gradually, which is why it's important to eat starch and sugar as part of whole foods, rather than in refined form.
No, because fruit includes a lot of fiber and releases the fructose into your digestive tract over time. Fruit juice is bad, though. It's essentially uncarbonated soda, and sometimes has a higher sugar content than soda. Compare grape juice to Mountain Dew, for example.
