The way that the DSP units work is very simple. The sound stream is made of samples, represented by floating-point values in the [-1.0, 1.0] range. Each unit has some input and output slots. A slot is made to transmit the data from/to a DSP unit. The number of these slots depend of the DSP unit. These numbers are fixed and are 0-based.
A DSP unit can be connected to other ones by connecting one of its output slot to one input slot of another DSP unit. The whole process is actually very simple. Once the connections are established, you can use the DSP construction that you have made.