Traps do not always work for rats at first, they're too smart. It's called "trap shy." They'll test them first. Your best bet is to get some rat bait and put it where they frequent. Find the nest and remove it if possible. Find out where they are coming in and repair it. If you want to try the traps, put food(peanut butter or anchovies work best) on but don't set it...yet. When they trust it, set it. Place the traps business end against the wall, as their runway is usually along the wall edges. When a trap has been successful, empty it and reset it...don't toss it yet. The smell of the rodent will be on the trap and will help attract others to it.