ive done paint correction/buffing for about 14 years now. always start with a thorough wash. when im going to be buffing i use dawn dish soap in my wash bucket. hit the wheel wells,rockers, and under the bumpers good with water to get any grit off the car. clean the jambs real good,too. i do that to get any grit that could come out when running the buffer-grit on the pad can wreak havoc.
then onto clay bar. i dont bother with the spray lubes that can come in a kit- i just put a few drops of dawn dishsoap in a buck and use that as the lube. do the entire car-even the glass.
i have a porter cable 7424- its a dual action buffer/polisher. impossible to screw up paint with it. doesnt build up heat. takes longer than a rotary. theres other brands on the market like it but i bought this 14 years ago and its still running strong.
pads- i use lake country CCS orange pads
Lake Country CCS Pads, lake country polishing pads, ccs buffing pads
for both cut and polish.
for products, ive been using meguiars since i started. i like to keep the same manufacturer for all detailing products as....welp....its quite overwhelming the amount of manufacturers and their detailing products. plus, meguiars has been working for me pretty good.
for the first pass i use meguiars M100
Meguiars M100 Pro Speed Compound
its designed for a will pad and rotary but it works great with the DA,too.
when im happy with the results i switch to megs m205 and the orange pads. m205 is a polish and pretty nice to work with.
Meguiars Mirror Glaze #205 Ultra Finishing Polish, final polish, Meguiars polishes, car polish, 205 FP

after that-especially on darker paints- i use megs #7 glaze
Meguiars #7 Show Car Glaze is a final step auto glaze to enhanced the gloss prior to wax application. Get a show car shine with Meguiars #7 Show Car
if i wasnt right there seeing the depth it adds i dont think id see it. but i like it.
then this wax
Meguiars #21 Synthetic Sealant 2.0

theres some good videos on the YT on using a DA polisher. heres one showing how safe they are
https://www.youtube.com/watch?v=2XAqpOe9Zt4

junkman has some good videos
https://www.youtube.com/watch?v=KP-eAddv2sk