Look for Forensic Detailing on YouTube, the guy is really good and does a lot of tutorials.Also, recently bought a £60 DA polisher from Argos, but haven't got the balls to use it on my car yet. Need to order some new pads for it and watch some YouTube videos!! Then I've got an unopened bottle of Collinite 845 to try. Swirl marks ahoy on my car so really want to learn how to polish it out.
You'll be hard pushed to do any damage at all with a DA polisher. My advice is to get a medium cutting pad (orange) for the cutting stage, then a black finishing pad for the polishing. Then a second black finishing pad for the Collinite 845. I've done this with mine and it works a treat.