One of the primary functions of a tenants policy is to insure your belongings against unforeseen loss or damage caused by an insured peril. Things like fire, theft, vandalism, or water damage etc., would be insured under a basic policy. If you want coverage for those perils, as well as things like mysterious disappearance, and accidental breakage, a more comprehensive policy would be the way to go.
If you have to move out of your home due to an insured loss, your tenants policy will cover the cost of necessary alternative living arrangements. It could also cover the cost of meals will you're out of your home.
Another important aspect of tenant insurance is liability coverage, both for in your home, and while you're away. If an accident occurs and you cause damage to not only your unit, but to other parts of the building, liability can protect your for the damages you caused. For example, if you left something in the oven which led to a fire, you could be held responsible for damages caused to any part of the building that you reside in. The same would apply if you are outside of your home and accidentally cause damage to another person or property.