The engine coolant level/temperature light came on in my 2007 volks. jetta..where do I put the coolant?

You put the coolant into the large plastic circular shaped reservoir with the large black plastic cap, near the firewall at the back of the engine, on the drivers side.

But it is very serious that you do not know where to put coolant, because that means it has never been checked.
Once it is over heated, then the thermostat also needs to be replaced.
You must also find out why it is low, since it should never be allowed to leak at all.
You need to perform a coolant system pressure check, with what is basically a pump that you replace the cap with.
You over pressurize it and watch for leaks that allow pressure to drop.
Then you start the engine, rev it up, and check for head gasket leaks that would cause pressure to oscillate.
The coolant light should never come on, and it is possibly very serious.