you usually won't find anything useful in a Fanuc manual for additional axis, only XYZ.
just set the center like any other work offset.
move tool to center of axis (using dial indicator etc) and set G54/55/56/57/58/59 etc to that position.
usually center of axis at top of part when clamped in chuck is X0 Y0 Z0.
rotary axis is usually addressed with A or B word.
A0 is position where rotary axis is at it's zero return position.
Programming rotary axis is not complicated because it's just a rotary movement.
So G00 A90.0 will rotate A axis 90 degrees. G00 A-90.0 will rotate axis 90 degrees in opposite direction.
Complex example can be something like......
G01 X2.5 Y-1.79 Z-0.500 A32.365
Sometimes additional M codes are required to enable the extra axis before issuing A command.
Or to pass control from main controller to additional axis controller. Then there is usually M commands to
clamp/unclamp rotate axis.
Exact programming depends on extra axis control type. See your additional axis controller manuals for the