If you take a thread and wrap up a bunch of it, so much it becomes a hill of thread, you're going to have a lot of thread. You can wrap some of that thread around other thread to create a much thicker thread. This thread is a cable.
You use this cable to swing down from a building but you need to do it soon (つな)! You're being chased by some bad guys and they've almost caught you, so if you're gonna swing to safety with this cable, you need to do it soon.