In order to customize OnStep's behavior to each users requirements there are a variety of configuration settings in the Config.h file.
Instead of editing the Config.h file manually, you can use the web based Online Configuration Generator which gets you a basic working file quickly by answering a few questions. You can later edit the same file further to add more options, when you need them.
If you are manually editing the file, then many settings are optional but those settings that must always match your hardware and must be set properly are highlighted in red. In some cases that's enough to get a working telescope controller but usually you also have to fill in the stepper driver information also, at a minimum, which is highlighted in yellow. In all cases you should only change the Value column of the Config.h file to the required selection.
There are numerous checks performed at compile time: Read the compiler warnings and errors, they are there to help guard against invalid configurations.
The Config.h file settings are categorized as follows:
Pinmap, configures OnStep for your controller hardware.
Mount Type, select from GEM, EQ Fork, or Alt/Az.
User Feedback, LED's and Speaker.
Time and Location, configures sources for getting time and location information.
Sensors, limit, PEC, home sense, etc.
ST4 Interface, set ST4 guide port behaviour, hand controller support, etc.
Guiding, turn off backlash during guides, limt guide duration for safety.
Tracking, automatically start tracking, backlash takeup rate, etc.
Slewing, set the default slew (goto) rate and if runtime changes to that rate should be remembered, slew acceleration settings.
Pier side, customize pier side and meridian flip handling.
Parking, allows "strict parking" where you can only unpark if the prior park was successful.
Step signal, wave form PULSE (for speed) or SQUARE (for better signal integrity.)
RA or Azm settings, steps per degree, step driver, step mode, etc.
Dec or Alt settings, steps per degree, step driver, step mode, etc.
Rotator (AXIS3) settings, steps per degree, etc.
Focuser 1 (AXIS4) settings, steps per micron, etc.
Focuser 2 (AXIS5) settings, steps per micron, etc.
Auxiliary Features, control switches, dew-heaters, etc.