First, RealPars has a video that shows you how to wire sinking and sourcing inputs:

A sinking digital I/O point (input/output) provides a grounded connection to the load. This means that the I/O card terminal is connected to ground internally, and it expects the load, the device connected to the input card, to provide power. So a sinking digital input or output card requires the connected device to be sourcing.

A sourcing digital I/O point provides a voltage source to the load. This means that the I/O card terminal is connected to 24 VDC internally, and it expects the load, the device connected to the input card, to sink the power to ground when actuated. So a sourcing digital input or output card requires the connected device to be sinking.