When an electron goes from ground state to excited state does it absorb or lose energy?
An electron absorbs energy when it goes from a ground state to an excited state.
This is the best graphic I can find to explain the process.
This absorption of energy is what causes the electron to jump levels. When the electron returns to ground state, the energy has to "Go" somewhere, so it is emitted as some type of energy. When you excite copper atoms, the emission occurs as the electron returns to a lower-energy state. This emission takes the form of visible, green light.
Think of an analogy of a child eating chocolate:
Absorption: The child eats the chocolate
Five minutes later: EMISSION
And back to ground state.
Also, keep in mind the Law of Conservation of Energy - Energy is absorbed by the electron. The requisite increase in energy must be emitted for the electron to return to ground state.