to explain what cycling a pond is, you need to understand the basics; very simply put, fish produce ammonia, which is toxic to them. Bacteria in your filter break down ammonia in to nitrites (also toxic to fish) and nitrites in to nitrates (which is fine, aka plant fertilizer). Now to get a reasonable amount of those bacteria in your filter, you need to feed them... ammonia. It takes a while before those bacteria colonize your filter and start breaking them down in to nitrites, and then the same for the bacteria that break down nitrites. Thats called a cycle.
You can do that with a few goldfish that you are not attached to, as they might die before your filter completes its cycle. Some add (tiny amounts!) of pure ammonia, but then be very sure to wait until it has "cycled" before adding any fish. you can also accelerate the process by buying filter bacteria in a bottle. Or.. you could use your turtle, which is unlikely to be harmed by ammonia or nitrites in anything but ridiculous quantities. Its actually a great idea.