Auto Insert date/time

What 'serial' does for auto incrementation of intgers,
are there something similar in PSQL where the db can
autoinsert the correct date/time data each time you
add a new row , without have to specify the code e.g.
Date() class in a java/C++ file? If well, how do I
manage to make this work? Is there maybe an PSQL
function which can do it? AN example will be nice :)

Big Thanks
Smith

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