How long will this UPS power my system when the power goes out?

Runtimes of any UPS will vary based on the amount of power required by your connected devices.

Will the UPS automatically switch off from the battery backup when power is restored?

Yes, when adequate power is restored to the UPS and is within the operating voltage range of the UPS, it will revert o passing utility power to connected electronics.

Will this UPS provide continuous power in the case of a power outage?

This Back-UPS has a typical transfer time of 6ms to 10ms to switch to battery power when the main power goes out. The transfer time is fast enough that most devices will not experience a power drop when the UPS transitions to battery power.

Can I plug the UPS to an extension cord or does it have to be plugged in to a wall outlet?

In order for your UPS to get the best power available, it should be plugged directly into the wall outlet. Plugging your UPS into a surge protector may cause the UPS to go to battery often when it normally should remain offline.