How can I access the GPIO on my BMD 300 (control them using basic methods like pinMode, digitalWrite? Do I need to download a new library to include in the IDE?
You mean this: www.rigado.com/.../ ?
Which says:
"The BMD-300 is based on the advanced nRF52832 BLE SoC from Nordic Semiconductor"
You will need to study the documentation from Nordic Semiconductor
www.nordicsemi.com/.../nRF52832
You should start with a Nordic Semi DevKit to gain familiarity ...
More likely that the OP means this:
www.rosa-moser.at/.../belle-minidumper-bmd-300-mit-honda-gxv1605.5kw
I hear it's got a well wicked control interface.