2Na + 2H2O -> 2NaOH + H2
To balance the equation, set up a chart as instructed:
On the left side, have the reactants with their starting amounts. On the left side, do the same with the products. Here, you should realize that Hydrogen has the odd number of 3. In order to make this an even number, add the coefficient of 2 to NaOH in order to get the new amounts.
Now that the products have even numbers, balance it on the reactants side. Take H2O and give it the coefficient of 2. This will give you four hydrogen and two oxygen. You now need to balance Sodium, and this can be done simply by adding the coefficient of 2 to the lone element.
Hope this helps!