It may not be your best alternative. Do you have a lack of hw in the restrooms? Consider an "on demand" remote heater. Sometimes with the existing piping a recirc will not help all fixtures.
Has this issue always existed- verify water heater is operating as it should first.
To answer your question as simply and short as possible though, hw leaves the tank, feeds all the fixtures then returns back to the cw inlet at the tank creating a loop. It also requires a pump and check valves to make the loop function
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