I know Rain powers up Water and weakens Fire vise versa for Sun but can other moves be boosted and weakened Ex:The sun is shining and I use thunder will the move be weakened?
No, Just that Thunder/Hurricane will have 50% Accuracy. Just that they cannot be boosted/weakened. Just fire moves and water moves.
Also, There is an exception. Solarbeam will have half the base power in hail,sandstorm and rain.