To see whether an equation is balanced, count each atom on each side of the equation.

Here, you have, on the left,
1 Na
3 O
1 H
1 C

and on the right:
1 Na
3 H
1 C
4 O

And as you can see, there are not the same number of atoms on each side, hence, the equation is not balanced.

Try putting some numbers in front of compounds to balance it. Can you balanced it? :)

Do you see your problem yet? You can't balance the equaion as written because NaOH + CO2 --> NaHCO3. Other than 0 there is no coefficient for H2O that will balance it. This makes sense because water is not a product when CO2 and NaOH react.