One thing you want to buy when cleaning a car is a clay bar.
You really wont believe the diffference in your paint the look and feel of it.
Basically as said spray the detailer over a panel and rub the bar of clay of the panels, keep needing it so stays reasonably clean and keep surface moist. when done each panel dry off and repeat if paint still feels a little rough.
After rub the back of your hand along the paint and feel how smooth "like glass"
rub ya hand on paint before then after.
Brilliant stuff