How does my Boiler work with my Baseboard and thermostat
Most likely, the thermostat simply actuates a valve, which allows hot water to flow through your radiator.  There's likely a main central circulation loop, with individual "heating loops" for each unit branching off. When your thermostat calls for heat, the valve allows the hot water to flow through your "heating loop".

As for what type of thermostat you can use, that completely depends on the system, the building, and the lease agreement.