Timothyz is spot on. Step/Dir is the interface to external drivers. The section in the WiKi is short because the interface is simple, and "just works".
He is also correct that the built in drivers are likely better, AND the firmware has SPI access to them, so it can set current, detect faults, etc.
Can you link to the motors, and particularly the drivers, so we can look at them in more detial?