If you want to know about differential thermostats, what they are and what they are used for, take a look at this page:
The differential thermostat is strictly necessary in a solar heating equipment.
Obviously it will not be necessary in a thermosyphon type solar heater.
The differential thermostat is the one who manages the pump according to the data received by the temperature probes.
So there is not much need to instruct too much on its installation, more when there is already documentation about it in the thermostats section.
Here I indicate the order of connections that the differential thermostat needs:
The graphic representation of the parts that connect with the solar thermostat: