Ironing is one of those settings on the Centauri Carbon that can make the top of a print look way better, but it can also make things worse if you get too aggressive with it. Basically, ironing has the nozzle make another pass over the top surface while pushing out a tiny amount of filament. The idea is to fill in those little gaps between the top lines and give you a much smoother finish.
For the Centauri Carbon, I'd start pretty conservative. A good starting point with PLA is around 20–30 mm/s ironing speed, 10–15% ironing flow, and about 0.1–0.15mm ironing line spacing. I wouldn't treat those numbers as some magic perfect setting though. Filament, temperature, layer height, and even the model you're printing can change what works best.
I'd probably start with 25 mm/s speed, 10% flow, and 0.1mm spacing and print a small ironing test before messing with a big model. If you're still seeing gaps between the ironing lines, bump the flow up a little. If the surface starts looking rough or like the nozzle is dragging too much plastic around, bring the flow back down.
Another thing I'd recommend is only ironing the topmost surfaces unless you have a specific reason to do otherwise. Ironing every top surface can add a surprising amount of print time, and most of those surfaces may never even be visible.
Don't expect ironing to fix a bad top layer either. You still want enough top layers and good extrusion underneath it. If your top surface already has gaps, pillowing, or obvious extrusion problems, I'd fix that first and then start playing with ironing.
I've found ironing is most useful on prints with big flat surfaces where those normal extrusion lines really stand out. Signs, boxes, lids, plaques, and other flat parts can look noticeably cleaner with it turned on. On detailed or curved models, I usually don't think it's worth the extra print time.
The biggest thing is to experiment with it. Run a small test with your actual filament and change one setting at a time. Once you find a Centauri Carbon ironing setting that works with the filament you normally use, save it as a profile so you don't have to figure it out all over again next time.