The spacecraft has two small, sealed tanks. One contains some form of Hydrazine (fuel) and the other Nitrogen Tetroxide (oxidizer) in liquid form. When those two liquids combine they ignite without an external ignition source (they are hypergolic), which makes them extremely reliable. The Specific Impulse for those two liquids is quite high so the thrusters only need to fire a small impulse. The craft only needs to have a very small rotational speed since time is not a factor and then the thruster that is 180 degrees opposite fires to stop the rotation.
Using such small amounts of fuel/oxidizer allows for many years of operation.
My late father retired from (Aerojet) Rocketdyne, the manufacturer of these thrusters, and I worked there for 13 years. He spent a lot of years on the manufacturing floor and would have been proud as Punch to hear about this. Rest in peace, Dad.