Type gems like fire gems,water gems,electric gems,or grass gems.I also mean moves like rain Dance,or sunny day? How much power do these items/moves up the power of a certain type move?
It multiplys by 50%
Sunlight: Increases the power of Fire-type moves by 50%.
Rain: Increases the power of Water-type moves by 50%.
The other two weathers dont increase the power of moves but they do have effects which can be found Here.