Ordering the lumber with one edge ripped on the rough-sawn board facilitates the initial milling steps.
Spiral cutter heads with indexed carbide cutters are more expensive, but they prevent chip-out and tear-out.
First, one face of the board is flattened. With one edge riding against the jointer fence, the board is fed face down across the jointer blade.
After several passes on the jointer, the rough areas have gotten smaller, but the board is not quite ready.
The now-smooth ripped edge is 90 degrees to the flattened face and can be run against the table saw's fence.
After the jointer, the board is run through a powerful thickness planer that quickly hogs material off the rough side. It takes several passes before that side is smooth enough to be run through a less powerful, but more precise planer.