Can you cook two things in the oven at the same time? And will it take longer? How much longer? Like can you roast a chicken and carrots on the other rack?
Yes, but it will take longer. Also, keep in mind that if you're roasting, what is on the top rack will "roast" directly (since the top heating element will be on) and this could block some of that roasting action from the bottom rack.
Similarly, if you're baking, the lower rack will get the most heat.