Some good guides:
There are a lot of "right" ways to detail a car (even more "wrong" ways though). Tons of products out there, and different detailers like different products. DetailedImage and DetailersDomain should have just about everything you need though.
Masking the edges is typically done before a polish/paint correction with a rotary/orbital. It's to prevent the spinning pad from hitting parts of the car it shouldn't - such as emblems, grilles, window trim, headlights, taillights, etc.
'15 i3 REX // Capparis // ZGW // ZTD // HK // 20"
20% Tint, Coding, LED High Beams/Signals, Painted Reflectors, MAX2 Hardwire
Past: F30 335i, E90 328xi