You have to combine each element on each side together.
You would do
1-Na-1 because there is 1 Na on each side
2-H-3 because there is 2 H on one side and 3 H on the other side
1-O-1 because 1 O on one side and 1 O on the other
Your final answer would be 2Na+2H2O-->2NaOH+H2
Hope I could help! :)
