Hi,
this is a very simple test stack to simply enlight a few leds, i used 1.5 Volt 20mA leds. So with 3v3 from the GPIO pins you can calculate easy which resistor you need in series with a led.
I uses the Library from Michael Doub for which i'm thankfull !
You can use this as a start for a simple motor-stepper driver which needs:
a PWM pulse 1 and 0 sometimes 200us.
a DIR-ection 1 or 0
ms1, ms2, ms3 so you can change the step size from Full to 16th step with combinations of 0 and 1 on each input
Eventually you could also use SLEEP and/OR ENABLE to shutoff the FET output's or the complete driver.
i bought a little driver board for 15,- euro with an A4998 ic, but you can get them for 2 euro/dollar on one of the chinese webshops, completely assembled (it's a tiny board, you can't solder the ic by hand, too little)
More next time.