to work in the correct or intended way
function normally/correctly/properly etc
Flights in and out of Taipei are functioning normally again.
Her legs have now ceased to function.
You know I can't function (=cannot perform normal activities) without a coffee in the morning.
if something functions in a particular way, it works in that way:
an understanding of how the economy functions
function as somethingphrasal verb
A library is functioning as a temporary hospital to cope with casualties.