Automatically the system turns on heater to dry up or suck out fluid/juices from the fruit.
#2 Can you slide out some trays & use to rise bread dough prior to baking in an oven?
The trays are removable. I dont see why you couldnt. You can adjust to temp accordingly but i would def keep an eye on it to ensure its not drying out the dough.
#3 Does it come with any sheets or do wehaveto buy em separately?
It comes with 6 trays, a drip tray, and a candy sheet
I tried to dry thin sliced oranges and after 18 hours I did not have what I’d like. 15 hours for thin sliced bananas and they were perfect. It takes time. I suggest using the same fruit or veggie on every tray, or just a few trays. Don’t mix multiple items. This 6 tray dehydrator is huge.