This is an example of how to get different temperatures from a set temperature heat source. This is an example of how to use a Gas Boiler to produce different water temperatures for 4 zones (High / Low Temperatures). You could also use an Electric Boiler, Propane Boiler or Oil Boiler in this configuration.
You will notice that in this example there are 3 possible water temperatures for the heating zones. There is 1 zone for high temperature that can feed hydronic radiators or hydronic baseboard convectors at whatever the boiler temperatures is set to. There are 2 zones for a set temperature that could be used for pex radiant floor heat zones at 2 different water temperatures.
This is only an example. Actual layouts vary from job to job.